Maryland Form 510, the Pass-Through Entity Income Tax Return (COM/RAD-069), is the information return that every partnership, S corporation, multi-member LLC, and business trust doing business in Maryland files with the Comptroller of Maryland to report income and pay tax on behalf of its nonresident members. You file Form 510 when your entity is not electing to pay Maryland tax at the entity level on every member’s share, which is the path that uses the separate Form 511 instead.
This guide walks you through the 2025 Form 510 line by line, using the figures and rates printed in the official 2025 PTE Booklet. Every Maryland pass-through entity must file, even one with no income or an inactive year, and missing the deadline triggers interest at a steep 10.8133% per year (about 0.9011% per month). Get the wrong return type and you can lock your entity into the wrong tax treatment for the whole year, because the choice between Form 510 and Form 511 is irrevocable once made on your first filing.
Here is what you will learn in this guide:
- 🧾 How to tell whether you file Form 510 or Form 511, and why the order of filings matters
- 📊 How to complete every line, box, and schedule with named, dollar-by-dollar examples
- 🧮 How to figure nonresident tax at the 2025 rates of 6.50%, 2.25%, and 8.25%
- 🗂️ Which documents, ID numbers, and federal figures to gather before you start
- ⚠️ The field-level mistakes that delay processing, trigger penalties, or cost members their credit
What the Form Is and Who Must File It
Form 510 is an information return with a tax-collection job attached. The pass-through entity itself usually pays no Maryland income tax on its own profit, because that profit flows through to the members, who report it on their own returns. The form’s real teeth show up when the entity has nonresident members, because then the entity must pay Maryland tax on those members’ shares before the money leaves the state.
The Maryland statute defines a “pass-through entity” to include partnerships under IRC Section 761, S corporations under IRC Sections 1361 and 1362, LLCs under the Maryland Corporations and Associations Article Section 4A-101, and business trusts under Section 12-101, per the 2025 Form 510 instructions. A single-member LLC that is disregarded for federal tax does not file its own Form 510, because its income lands on the owner’s return instead. Ignoring the filing duty has a direct consequence: the Comptroller can assess penalties and disallow member-level credits that should have flowed through the entity.
Every Maryland PTE must file, even with zero income or an inactive year, and a “letter in lieu of filing” will not be accepted. One common misconception is that an out-of-state LLC with a few Maryland customers always has to file. The instructions say a multistate PTE that operates in Maryland but is not subject to Maryland income tax law is not required to file, though it may file a zero return for the record.
Form 510 vs. Form 511: The Choice That Drives Everything
The single biggest decision is which return you file, because it is binding for the year. Form 510 means you are not making the pass-through entity tax (PTET) election, so you pay tax only on nonresident members’ shares. Form 511 means you are electing to pay Maryland tax at the entity level on all members’ shares, resident and nonresident alike, which is what lets owners work around the federal SALT cap.
| Feature | Form 510 (No PTET Election) | Form 511 (PTET Election) |
|---|---|---|
| Who pays tax | Entity pays on nonresident shares only | Entity pays on all members’ shares |
| The election | Not made; default treatment | Made and irrevocable for the year |
| First filing of the year | Filing 510 first locks in non-election | Made on Form 510/511D or 510/511E |
| SALT-cap workaround | Not available to resident members | Available to all members |
| Year-end return | Form 510 | Form 511 |
The instructions are blunt: if your first filing of the tax year is Form 510, that is “deemed to be an irrevocable decision to pay tax only on behalf of nonresident members.” You also may not file an amended return to change your election or non-election after the fact.
Before You Start: Documents and Information You Need
Maryland Form 510 is built on top of your finished federal return, so you cannot complete it accurately until the federal numbers are locked. The instructions say to “complete the federal income tax return first and use it in preparation of the Maryland return.” Rushing the state form before the federal numbers settle is the most common reason filers have to amend.
Gather these items before you open the form:
- Federal return (Form 1065 or 1120S) with Schedule K. You pull the distributive or pro rata share of income straight from it, and the wrong federal figure flows into every Maryland calculation.
- Federal Employer Identification Number (FEIN). This nine-digit number ties your return to your account, and a missing or wrong FEIN sends your filing to the wrong place or stalls it.
- Date of organization or incorporation. It is entered as MMDDYY, and the form asks for it directly near the top.
- Six-digit business activity code. It comes from your federal return and identifies your principal activity.
- Complete member roster with residency status. You need each member’s name, SSN or FEIN, address, ownership percentage, and resident or nonresident status, because Schedule B is built from this list.
- Each member’s distributive or pro rata share of income. Without per-member shares you cannot allocate income or compute nonresident tax.
- Apportionment data (multistate entities). Maryland and total receipts (and property and payroll if you sell intangibles) feed Schedule A; missing data forces a guess that invites audit.
- Estimated payment records (Form 510/511D) and any extension payment (Form 510/511E). These reduce your balance due, and forgetting them means you overpay or double-pay.
- Prior-year overpayment carryforward amount. It counts as a payment on Line 16a, and skipping it inflates your balance due.
- Any Schedule K-1 (510/511) received from another PTE. This supports credit for tax another entity already paid on your behalf.
Skipping any one of these items usually means a wrong line entry, a delayed refund, or an amended return. Treat this checklist as the gate you pass through before writing a single number on the form.
Where to Get the Form and How to Access It
You get the official Form 510 and its instruction booklet from the Comptroller of Maryland’s website. The current package is the 2025 PTE Booklet 510, which carries the form number COM/RAD-069 and the preprinted tax year. Always confirm the preprinted year matches the year your tax period begins, because the instructions require the form to “reflect the preprinted tax year in which the PTE’s tax year begins.”
Maryland strongly pushes electronic filing through the Federal/State Modernized e-File (MeF) program, and for some entities it is mandatory. The instructions state that Form 510 “must be filed electronically if the pass-through entity has generated a business tax credit from Form 500CR or a Maryland Historic Revitalization Tax Credit from Form 502S to pass on to its members.” Most commercial tax software supports Maryland PTE e-filing, and you can reach the Comptroller’s e-File Help Desk by emailing efil@marylandtaxes.gov.
If you file on paper, use blue or black ink only, and do not use pencil, colored ink, colored paper, or staple or punch holes through the barcode. These rules sound fussy, but writing in the wrong color or damaging the barcode slows machine processing and can bounce your return. You may also use an approved computer-generated substitute form, but only if the Revenue Administration Division approved it in advance.
Step-by-Step: How to Fill Out Maryland Form 510 Line by Line
This is the heart of the return. Work top to bottom, and remember that lines 5 through 19 are skipped entirely unless your entity has nonresident members. Each field below uses the exact label and box number printed on the official form.
Top of Form: Tax Year, FEIN, and Entity Identity
This header block tells the Comptroller who is filing and for what period. You enter the FEIN, the date of organization or incorporation (MMDDYY), the six-digit business activity code, and the entity’s exact legal name and mailing address. If your tax year is not a calendar year, you write the beginning and ending fiscal dates in the space at the top.
Enter the FEIN exactly as the IRS issued it; if you applied but have no number yet, write APPLIED FOR followed by the application date. For example, Coastal Bay Oysters LLC enters its FEIN 52-1234567, its organization date 03/14/19, and its name precisely as registered with the state.
A common edge case is the “Trading As” name. If your entity operates under a T/A or DBA, enter the legal name first and continue with the T/A name, because the Comptroller matches the legal name to your account. A frequent mistake here is entering a tax-prep firm’s address instead of the entity’s address, which routes notices to the wrong place and delays your response window. The misconception to drop is that the name only needs to be “close enough”; the Comptroller cross-references the exact registered name, and a mismatch can hold up processing.
Type of Entity Box
This box asks what kind of pass-through entity you are. You check exactly one box: S Corporation, Partnership, Limited Liability Company, or Business Trust. The choice controls which federal rules and Schedule K lines Maryland expects you to follow.
For example, Three Rivers Consulting, an S corporation, checks the S Corporation box, while a multi-member LLC taxed as a partnership checks Limited Liability Company. The nuance: an LLC taxed as a partnership for federal purposes still follows partnership rules throughout the form, even though you check the LLC box. A common mistake is checking S Corporation for an LLC that merely elected S status while leaving the federal treatment mismatched, which confuses the income source lines. The misconception to discard is that “LLC” and “partnership” are interchangeable boxes; they are not, and the box must match your actual federal classification.
“Check Here” Status Boxes
These boxes flag special situations about the filing. You check any that apply: Name or address has changed, First filing of the entity, Inactive entity, Final Return, 510C Filed, Amended Return, or the box for a tax year with different dates due to an acquisition or consolidation. Each box changes how the Comptroller treats your account.
For example, a newly formed partnership filing its first Maryland return checks First filing of the entity. The nuance: do not check Inactive or Final if the PTE is inactive in Maryland but still active elsewhere, because that wrongly signals the entity has shut down. A common mistake is forgetting to check Final Return when the entity dissolves, which leaves the account open and generates non-filing notices in later years. The misconception to drop is that these boxes are optional housekeeping; they directly drive notices, account status, and whether Maryland expects future returns.
Line 1 – Number of Members
This line counts your members by category. You enter the number of members that are Maryland-resident individuals (including resident fiduciaries) on 1a, individual nonresidents on 1b, nonresident entities on 1c, and “Others” (resident entities and tax-exempt entities) on 1d, then the total on 1e. The counts decide whether you owe any nonresident tax at all.
For example, Harbor Light Partners with two Maryland partners, one Virginia partner, and one out-of-state corporate partner enters 2 on 1a, 1 on 1b, 1 on 1c, and 4 on 1e. The nuance: a single-member LLC that is disregarded for federal tax is treated as an individual or a corporation depending on its owner, for counting purposes. A common mistake is putting resident entities in the wrong bucket; resident entities and tax-exempt entities go in “Others” on 1d, not with nonresident entities. The misconception to correct is that members and ownership percentages are the same thing; Line 1 counts people and entities, while later lines handle percentages.
Line 2 – Total Distributive or Pro Rata Share of Income
This line carries your total business income from the federal return. For partnerships, it is the net amount of lines 1 through 11 of federal Form 1065 Schedule K; for S corporations, it is the net of lines 1 through 10 of Form 1120S Schedule K, less interest from federal obligations. Unistate entities, and multistate entities with no nonresident members, also copy this amount down to Line 4.
For example, Coastal Bay Oysters LLC, a Maryland-only partnership, nets its Schedule K lines to $400,000 and enters that on Line 2. The nuance: you must subtract interest from federal obligations, because Maryland does not tax it. A common mistake is pulling ordinary business income from line 1 alone instead of the full net of the listed K lines, which understates income and triggers an adjustment. The misconception to drop is that you can re-characterize an item for Maryland; the character of every item must match the federal return.
Line 3a – Non-Maryland Income (Separate Accounting)
This line removes income earned outside Maryland when you use separate accounting. Multistate partnerships with nonresident partners, or multistate S corporations whose Maryland activity is nonunitary, may allocate income by separate accounting and enter the out-of-state amount here, attaching a worksheet. You then subtract Line 3a from Line 2 to reach Line 4.
For example, a consulting partnership that nets $500,000 total and earns $200,000 of it from clearly separate out-of-state operations enters $200,000 on Line 3a. The nuance: separate accounting is only allowed when activities are genuinely distinct and nonunitary; most multistate businesses must apportion on Line 3b instead. A common mistake is using separate accounting for a unitary business to shrink Maryland income, which the Comptroller will reverse on audit. The misconception to correct is that you can pick whichever method gives the lowest tax; the method must fit your actual business structure.
Line 3b – Maryland Apportionment Factor
This line applies your apportionment factor to spread income to Maryland. Multistate PTEs using apportionment compute the factor on the Schedule A worksheet, then multiply Line 2 by that factor and put the result on Line 4. Maryland generally uses a single receipts factor, so property and payroll factors are not required unless you have income from selling intangibles or fall under a special formula.
For example, Three Rivers Consulting, an S corporation with $1,000,000 of income and a Maryland receipts factor of 0.250000, multiplies and carries $250,000 to Line 4. The nuance: if the computed factor is zero, you must enter .000001 rather than leaving it blank or at zero. A common mistake is rounding the factor to fewer than six decimal places, which misstates Maryland income. The misconception to drop is that every multistate filer needs three factors; under current rules a service or product seller without intangible-sale income uses receipts only.
Line 4 – Distributive or Pro Rata Share of Income Allocable to Maryland
This line is the Maryland slice of income that drives the nonresident tax. Unistate PTEs, and multistate PTEs without nonresident members, simply enter the Line 2 amount. Multistate PTEs using separate accounting subtract Line 3a from Line 2, and those using apportionment carry down the Line 3b result.
For example, Coastal Bay Oysters LLC (unistate) copies its $400,000 from Line 2 to Line 4, while Three Rivers Consulting enters its apportioned $250,000. The nuance: this figure is the base for all nonresident tax math below, so an error here multiplies through every later line. A common mistake is forgetting to bring down the apportioned figure and instead using total income, which overpays nonresident tax. The misconception to correct is that Line 4 is the entity’s “taxable income”; it is the Maryland-allocable share that feeds the nonresident calculation, not a direct tax base for resident members.
Lines 5 through 9 – Nonresident Individual Tax
These lines calculate Maryland tax on nonresident individual members. On Line 5 you enter the total ownership percentage held by nonresident individuals (leave blank if 100%). Line 6 multiplies Line 4 by that percentage; Line 7 multiplies Line 6 by 6.50% (the 2025 rate); Line 8 multiplies Line 6 by the 2.25% special nonresident tax; and Line 9 adds Lines 7 and 8.
For example, Harbor Light Partners has nonresident individuals owning 25% of a $400,000 Maryland income base: Line 6 is $100,000, Line 7 is $6,500, Line 8 is $2,250, and Line 9 is $8,750. The nuance: if profit/loss sharing differs from ownership percentage, use the profit/loss percentage on Line 5. A common mistake is using last year’s 5.75% rate; for 2025 the top rate rose to 6.50%, and using the old rate underpays. The misconception to drop is that the 2.25% special tax is optional; every nonresident individual owes it on Maryland-allocable income.
Lines 10 through 13 – Nonresident Entity Tax and Total
These lines handle nonresident entity members and total the nonresident tax. Line 10 is the ownership percentage held by nonresident entities (blank if 100%); Line 11 multiplies Line 4 by that percentage; Line 12 multiplies Line 11 by 8.25%; and Line 13 adds Line 9 and Line 12 for total nonresident tax.
For example, if a nonresident corporation owns 25% of Harbor Light Partners’ $400,000 base, Line 11 is $100,000, Line 12 is $8,250, and Line 13 adds the $8,750 from Line 9 to reach $17,000. The nuance: a “nonresident entity” is one not formed under Maryland law and not registered to do business in Maryland. A common mistake is taxing a resident entity here; resident entities belong in “Others” and are not subject to this nonresident tax. The misconception to correct is that the 8.25% rate applies to all entity members; it applies only to nonresident entities, not to entities organized or registered in Maryland.
Lines 14 and 15 – Distributable Cash Flow Limitation and Tax Due
These lines can cap the nonresident tax based on cash flow. Line 14 holds the distributable cash flow limitation from Worksheet 9A, used only if you elect that method, and you check the box when you use it. Line 15 is the nonresident tax due: enter Line 13 if you do not use the limitation, or the lesser of Line 13 or Line 14 if you do.
For example, Harbor Light Partners with a Line 13 of $17,000 but a distributable cash flow limitation of $12,000 enters $12,000 on Line 15. The nuance: the limitation reduces what the entity must pay, but it does not reduce the members’ own tax liability. A common mistake is using the limitation without completing Worksheet 9A, leaving no support if audited. The misconception to drop is that the cash flow limit erases tax; it only defers the entity’s payment obligation, and members still owe their share.
Lines 16a through 16h – Payments and Credits
These lines gather everything already paid toward the tax. 16a is estimated tax paid with Form 510/511D plus any prior-year overpayment; 16b is the payment made with the Form 510/511E extension; 16c is tax paid on your behalf by another PTE; 16d through 16g capture entity-level credits and amended-return payments; and 16h totals 16a through 16g.
For example, if Harbor Light Partners paid $10,000 in estimates with Form 510/511D and $2,000 with its extension, Line 16a is $10,000, Line 16b is $2,000, and Line 16h is $12,000. The nuance: credit on 16c requires you to attach the Schedule K-1 (510/511) from the paying PTE as support. A common mistake is omitting estimated payments, which makes the return show a false balance due and triggers a needless payment. The misconception to correct is that prior-year overpayments are refunded automatically; you must enter the carryforward on 16a for it to count.
Lines 17 through 23 – Balance Due, Overpayment, Interest, and Refund
These final lines settle up. Line 17 is the balance of tax due when Line 15 exceeds Line 16h. Line 18 is the overpayment when payments exceed tax. Line 19 is interest and penalty from Form 500UP or late payment. Line 20 is the total nonresident balance due, and Lines 21 through 23 handle applying overpayment to 2026 estimates or requesting a refund.
For example, with $12,000 tax on Line 15 and $12,000 in payments on Line 16h, Harbor Light Partners shows $0 on both Line 17 and Line 18. The nuance: if you file late, interest runs at 10.8133% per year (about 0.9011% per month) on tax unpaid after the original due date. A common mistake is leaving Line 19 blank on a late return, which only delays the penalty to a later assessment. The misconception to drop is that an extension to file is an extension to pay; full payment is still due by the original deadline to avoid interest.
Schedule A – Computation of Apportionment Factor
Schedule A builds the factor used on Line 3b for multistate filers. You report receipts within Maryland (Column 1) and within and without Maryland (Column 2), then divide to a six-place decimal in Column 3. Most filers use the single receipts factor; property and payroll sections are completed only if you sell intangibles or fall under a special formula.
For example, Three Rivers Consulting with $500,000 of Maryland receipts and $2,000,000 total enters a factor of 0.250000. The nuance: special formulas apply to rental, transportation, financial, and manufacturing companies, so confirm whether one fits you. A common mistake is mixing total-company figures into the Maryland column, which inflates the factor. The misconception to correct is that gross receipts include everything; you use receipts less returns and allowances, matching the form’s line labels.
Schedule B – Members’ Information
Schedule B lists every member and their shares. Part I covers individuals (in SSN order), Part II covers fiduciaries, Part III covers pass-through entity members including S corporations, and Part IV covers C corporation members, all in the order the form requires. For each you enter the name, ID number, address, residency, and the distributive shares of income, tax paid, and credit.
For example, Coastal Bay Oysters LLC lists each Maryland partner in Part I with the Resident box checked and that partner’s share of income. The nuance: you must file Form 510 electronically to pass on business tax credits from Form 500CR or Form 502S to members through Schedule B. A common mistake is listing members out of order or omitting a member, which breaks the cross-check against the K-1s. The misconception to drop is that Schedule B is optional detail; it is the backbone the Comptroller uses to verify each member’s flow-through amounts.
Three Filled-Out Examples Using Real Scenarios
These three walkthroughs follow named filers through the most common Form 510 situations. Each shows what goes on the major lines so you can match your facts to the closest pattern.
Scenario 1: Coastal Bay Oysters LLC — Maryland-Only, All Resident Members
Coastal Bay Oysters LLC is a two-member LLC taxed as a partnership, with both members living in Maryland and all business inside the state. Because there are no nonresident members, it skips the nonresident tax lines entirely and files mostly as an information return.
| Form Section | What Coastal Bay Oysters Enters |
|---|---|
| Type of Entity box | Checks Limited Liability Company |
| Line 1a / 1e | 2 residents / total 2 |
| Line 1b, 1c | Blank (no nonresidents) |
| Line 2 | $400,000 total income |
| Allocation area (3a/3b) | Left blank (unistate) |
| Line 4 | $400,000 allocable to Maryland |
| Lines 5–19 | Skipped (no nonresident members) |
| Schedule B Part I | Both members listed, Resident box checked |
| Signature block | Signed by managing member |
Scenario 2: Three Rivers Consulting — Multistate S Corp with Nonresident Members
Three Rivers Consulting is an S corporation operating in three states, with shareholders in Maryland and Pennsylvania. It must apportion income to Maryland and pay nonresident tax on its Pennsylvania shareholders’ shares.
| Form Section | What Three Rivers Consulting Enters |
|---|---|
| Type of Entity box | Checks S Corporation |
| Line 1a / 1b / 1e | 2 residents / 2 nonresidents / total 4 |
| Line 2 | $1,000,000 total income |
| Schedule A factor → Line 3b | 0.250000 |
| Line 4 | $250,000 allocable to Maryland |
| Line 5 / Line 6 | 50% / $125,000 |
| Line 7 / Line 8 / Line 9 | $8,125 / $2,812.50 / $10,937.50 |
| Line 16a | $11,000 estimated tax paid with 510/511D |
| Line 17 | Balance due after payments |
Scenario 3: Harbor Light Partners — Mixed Resident, Nonresident, and Entity Members
Harbor Light Partners is a Maryland partnership with two resident individuals, one nonresident individual, and one nonresident corporate partner. It must compute both nonresident individual tax and nonresident entity tax.
| Form Section | What Harbor Light Partners Enters |
|---|---|
| Type of Entity box | Checks Partnership |
| Line 1a / 1b / 1c / 1e | 2 / 1 / 1 / total 4 |
| Line 2 and Line 4 | $400,000 (unistate) |
| Line 5 / Line 6 | 25% / $100,000 |
| Line 7 / Line 8 / Line 9 | $6,500 / $2,250 / $8,750 |
| Line 10 / Line 11 / Line 12 | 25% / $100,000 / $8,250 |
| Line 13 | $17,000 total nonresident tax |
| Line 16a / 16b / 16h | $10,000 / $2,000 / $12,000 |
| Line 17 | $5,000 balance due |
How to File the Completed Form
Maryland accepts Form 510 by electronic filing and by mail, and e-filing is required in some cases. Choose your channel based on whether you are passing through tax credits and on your software setup.
- Electronic filing (MeF). File through approved tax software in the Federal/State Modernized e-File program. This channel is mandatory if you generated a Form 500CR business credit or a Form 502S Historic Revitalization credit to pass to members. There is no separate state filing fee for the return itself; pay any balance by the software’s supported methods, and keep the e-file acknowledgment as proof of filing. Processing is faster than paper, often within a few weeks.
- By mail. Send the paper return, with all Schedule B pages and attachments, to the Comptroller of Maryland, Revenue Administration Division, 110 Carroll Street, Annapolis, Maryland 21411-0001. Make checks payable to “Comptroller of Maryland” and write your FEIN on the check in blue or black ink. Keep a copy of the full return and a certified-mail or tracking receipt as your proof of filing. Paper processing takes longer, so allow extra weeks.
For an extension, file Form 510/511E by the original due date; this grants seven months for S corporations and six months for other PTEs, but only if you also have a federal extension and pay any balance due with the request. You can submit the extension through Maryland’s online business extension system. Remember that the extension covers filing, not payment.
What Happens After You File
After Maryland receives Form 510, the Revenue Administration Division posts your return and applies any payments to your account. If you e-filed, your acknowledgment confirms acceptance; if you mailed it, allow several weeks before the account updates. The members then report their flow-through income on their own Maryland returns and claim credit for the nonresident tax the entity paid.
All items on Form 510 are subject to audit and revision for three years from the later of the due date (including extensions) or the filing date. If the Comptroller adjusts your return, you receive a notice, and you have 30 days to request an informal hearing with the Compliance Division. Missing that 30-day window makes the assessment final and non-appealable, so calendar it immediately.
If the IRS later changes your federal return, you must submit a copy of the final IRS adjustment report within 90 days and file an amended Maryland return. Members may then need to amend their own returns too. The entity must also give members a revised Schedule K-1 (510/511) so their numbers stay consistent with the corrected entity figures.
Mistakes to Avoid When Filling Out the Form
Form 510 has many fields, and each one is a chance to slip. These are the errors that most often cause delays, penalties, or lost member credits.
- Filing Form 510 when you meant to elect PTET. The election is irrevocable, so a wrong first filing locks you out of the SALT-cap benefit for the year.
- Using the old 5.75% nonresident rate. The 2025 top rate is 6.50%, and using last year’s rate underpays and triggers interest.
- Forgetting the 2.25% special nonresident tax on Line 8. Skipping it understates tax due on every nonresident individual.
- Applying 8.25% to a resident entity. Only nonresident entities owe that rate, so taxing a Maryland entity overpays and misreports.
- Carrying total income to Line 4 instead of the apportioned amount. This overstates the Maryland base and overpays nonresident tax.
- Entering zero apportionment factor instead of .000001. A literal zero misstates the factor and conflicts with the instructions.
- Omitting estimated payments on Line 16a. This produces a false balance due and a duplicate payment.
- Skipping the prior-year overpayment carryforward. It will not apply on its own and inflates your balance.
- Leaving members off Schedule B or listing them out of order. This breaks the cross-check with the K-1s and can delay processing.
- Stapling or punching the barcode on a paper return. Damaging the barcode slows or stops machine processing.
- Treating an extension as more time to pay. Interest still accrues on unpaid tax from the original due date.
- Filing on paper when a Form 500CR credit is involved. Passing those credits to members requires electronic filing.
Do’s and Don’ts
Keep these habits in mind to file a clean return the first time.
- Do finish your federal return first, because every Maryland figure flows from it.
- Do confirm the preprinted tax year matches the year your tax period begins, so the form is the correct version.
- Do check exactly one entity-type box that matches your federal classification.
- Do use the 2025 rates of 6.50%, 2.25%, and 8.25% in the right spots.
- Do attach the supporting Schedule K-1 (510/511) when you claim credit on Line 16c.
- Do keep your e-file acknowledgment or certified-mail receipt as proof of filing.
- Don’t file Form 510 if you intend to make the PTET election, because the choice is irrevocable.
- Don’t use pencil, colored ink, or colored paper on a paper return.
- Don’t leave Line 1 member counts blank, since they decide whether nonresident tax applies.
- Don’t skip Schedule B, which the Comptroller uses to verify member shares.
- Don’t assume an extension delays payment, because interest runs from the original due date.
- Don’t file a “letter in lieu” of the return, since Maryland will not accept it.
Pros and Cons of Filing on Your Own vs. With Help
Many small entities can file Form 510 themselves, but multistate and credit-heavy returns often justify professional help. Weigh the trade-offs against your situation.
| Filing on Your Own | Filing With a Professional |
|---|---|
| Saves preparer fees, which helps a simple Maryland-only entity | Costs a fee, but reduces costly errors on complex returns |
| You control timing and learn your own numbers | A CPA knows the 510-versus-511 election traps cold |
| Fine for unistate, all-resident entities with simple income | Better for multistate apportionment and Schedule A work |
| Works well when you have no nonresident members | Handles nonresident tax math and credit pass-through cleanly |
| Quick for an inactive or zero-income required filing | Helps when Form 500CR credits force electronic filing |
The pros of self-filing are real for a Coastal Bay Oysters-style return: low cost, full control, and a short form. The cons appear fast once you add nonresident members, apportionment, or business credits, where a single wrong rate or a mishandled election can cost far more than a preparer’s fee.
FAQs
Do I file Form 510 or Form 511?
No single answer fits all. File Form 510 if you are not electing entity-level tax on all members; file Form 511 if you make the irrevocable PTET election to pay tax on every member’s share.
Is filing Form 510 required even if my entity had no income?
Yes. Every Maryland pass-through entity must file, including inactive or zero-income entities, and the Comptroller will not accept a letter in lieu of the return.
Is the nonresident individual tax rate still 5.75% for 2025?
No. For tax year 2025 the top rate rose to 6.50% on Line 7, plus the separate 2.25% special nonresident tax on Line 8.
Do I check the S Corporation box or the LLC box for an LLC taxed as an S corp?
Yes, check the box matching your federal classification; an LLC that elected and is treated as an S corporation for federal tax checks S Corporation, not LLC.
Do I count resident corporate members on Line 1c?
No. Line 1c is only for nonresident entities; resident entities and tax-exempt entities go in “Others” on Line 1d instead.
Do I enter zero on Line 3b if my apportionment factor is zero?
No. If the factor computes to zero, enter .000001 on Line 3b, because a literal zero conflicts with the instructions.
Do unistate entities complete the allocation lines 3a and 3b?
No. Unistate entities, and multistate entities with no nonresident members, skip the allocation area and carry Line 2 straight to Line 4.
Is an extension to file also an extension to pay?
No. Form 510/511E extends only the filing deadline; full payment of any balance is still due by the original due date or interest accrues.
Do I have to file electronically?
Yes, in some cases. Electronic filing is mandatory if you generated a Form 500CR business credit or a Form 502S Historic Revitalization credit to pass to members.
Can I amend Form 510 to change my election after filing?
No. You may not file an amended return to change the entity’s election or non-election for the tax year once it is made.
Do I attach anything to claim credit for tax another PTE paid on my behalf?
Yes. Attach the Maryland Schedule K-1 (510/511) or statement from the paying PTE to support the credit you enter on Line 16c.
Is the 8.25% rate applied to all entity members?
No. The 8.25% rate applies only to nonresident entity members on Lines 11 and 12, not to resident or Maryland-registered entities.
When is Form 510 due?
Yes, there is a fixed deadline: file by the 15th day of the 4th month after the close of your tax year, which is April 15 for calendar-year filers.
Do I skip lines 5 through 19 if I have no nonresident members?
Yes. Lines 5 through 19 are completed only when there is an entry on Line 1b or Line 1c; with all-resident members you skip them.
Related reading
- How to Fill Out Maryland Form 500 (w/Examples) + FAQs
- How to Fill Out Maryland Form 502UP (w/Examples) + FAQs
- How to Fill Out Maryland Form 504 (w/Examples) + FAQs
- How to Fill Out Maryland Form 504NR (w/Examples) + FAQs
- How to Fill Out Maryland Form 505 (w/Examples) + FAQs
- How to Fill Out the Maryland SDAT Annual Report and Personal Property Return (Form 1) + FAQs
- How to Fill Out Maryland Form 502SU (w/Examples) + FAQs