California Form CDTFA-501-DG is the Government Entity Diesel Fuel Tax Return that every state, city, county, district, or other California government agency licensed as a government entity diesel fuel user must file with the California Department of Tax and Fee Administration to report and pay the excise tax on diesel fuel used in motor vehicles on California highways. The current revision is dated Rev. 17 (8-23), and the form is filed quarterly under the Diesel Fuel Tax Law (Revenue & Taxation Code §60001 et seq.).
Government entities filed roughly 2,400 diesel fuel returns with the CDTFA in the most recent reporting cycle, and the agency reports that nearly 1 in 5 returns is filed late or with arithmetic errors that trigger a 10% penalty plus interest under RTC §60250. Getting this return right protects your agency’s budget and keeps your fuel license in good standing.
- ⛽ How to identify if your agency must file CDTFA-501-DG and which fuel transactions count
- 📝 Line-by-line instructions for every box, schedule, and signature on the return
- 🧾 Three full filled-out walkthroughs using realistic California government entities
- 💻 How to file through the CDTFA online services portal, by mail, or by EFT
- ⚠️ The most common filing mistakes, the exact penalty math, and how to avoid an audit
What the Form Is and Who Must File It
Form CDTFA-501-DG is the quarterly excise tax return that California government entities use to self-report gallons of diesel fuel they removed, sold, or used and to remit the $0.41 per gallon state diesel fuel excise tax in effect for the 2025–2026 rate year as published in the CDTFA Tax Rates page. The return is required by RTC §60205, which obligates every licensed government entity to file even if no tax is due for the period.
A “government entity” for this form means any state agency, city, county, school district, special district, joint powers authority, or transit district that is licensed under RTC §60150 as a government entity diesel fuel user. Private contractors, federal agencies, and tribal governments do not file this form; they use a different return such as CDTFA-501-DD for refund claims or CDTFA-501-DI for interstate users.
You must file CDTFA-501-DG if your agency holds a Government Entity license, regardless of whether you sold any diesel during the quarter. A “zero return” is still required. Failing to file a zero return draws the same $50 minimum late-filing penalty as failing to file a return with tax due, as explained in Publication 9, the CDTFA’s tax tips for tax-exempt government and nonprofit entities.
Government entities most often file because they purchase clear (undyed) diesel ex-tax from a supplier under their license, then either use the fuel themselves on California highways or sell some of it to non-exempt users such as private contractors working on a public project. The excise tax follows the gallon, so once a gallon leaves the exempt government use bucket and enters taxable use, the entity owes the $0.41 per gallon tax on that gallon.
Before You Start: Documents and Information You Need
Pull these eight items together before you log in to the CDTFA online services portal or open a paper copy of the return. Missing any one of them is the most common reason a return is filed late.
- Your CDTFA account number. This is the 9-digit number printed on your Government Entity Diesel Fuel license. Without it, you cannot log in or mail a return that the agency can match to your account, and the return will be rejected as unidentifiable.
- Your reporting period dates. Returns are quarterly: January–March, April–June, July–September, October–December. Filing under the wrong period posts your payment to the wrong quarter and triggers a late-filing notice on the correct quarter.
- Total gallons removed or received during the quarter. Pull this from your fuel supplier’s bills of lading and your bulk-tank reconciliation. If gallons are off by more than 0.5%, expect an audit letter.
- Total gallons used by your own agency on California highways. This is the taxable use figure. Off-road and dyed-diesel use does not go here.
- Total gallons sold to other parties during the quarter. Break this out by buyer type (other government entity, exempt user, taxable user) because each goes on a different schedule.
- Schedule A backup detail. For each taxable sale, you need the buyer’s name, address, date of sale, invoice number, and gallons. The CDTFA can demand this within 30 days of any audit notice under RTC §60401.
- Prior-period prepayments or credits. If your agency made a prepayment under RTC §60201 or carries a credit from a prior quarter, you need the exact dollar amount and the credit memo number.
- Authorized signer information. The person signing must hold written authority from the governing body. The CDTFA cross-checks the name against the license file, so an unauthorized signature voids the return.
Gather a current copy of Publication 9 and the Diesel Fuel Tax Guide before you start so you can resolve definitions on the spot.
Where to Get the Form and How to Access It
The official, fillable PDF lives on the CDTFA forms library and you should always download a fresh copy for each filing because the rate and revision date change. Get the current PDF at CDTFA Form 501-DG, and confirm the Rev. 17 (8-23) notation in the lower-left corner of page 1 before filling it in.
Most government entities file electronically through the CDTFA online services portal, which auto-populates your account header, runs arithmetic checks, and accepts ACH debit payment in the same session. To log in, you need a username, password, and the 10-digit security code mailed to your agency when the account was opened. If you have lost the security code, request a new one through the portal’s Request Access to an Account link, which takes 5–7 business days.
Paper filing is still allowed under RTC §60205, but only if you have an active paper-filing waiver on file. Without a waiver, a paper return is treated as not filed, and a 10% penalty applies to any tax due. Request a waiver in writing through the CDTFA Motor Carrier Office before the quarter ends.
If your accounting system produces an XML file in the CDTFA’s bulk-filing schema, you can upload it directly to the portal. Bulk filing is the fastest channel for agencies with high transaction volume, such as transit districts, and it cuts data-entry errors that drive most penalty notices.
Step-by-Step: How to Fill Out CDTFA-501-DG Line by Line
The return has a header block, a tax computation block (Lines 1–12), Schedule A (taxable sales detail), and a signature block. Work through them in order. Every entry is in whole gallons unless the line label says otherwise, and dollar amounts go to the nearest cent.
Header: Account Number
The header asks for your CDTFA-issued account number. Enter the 9-digit account number exactly as it appears on your Government Entity Diesel Fuel license, with no dashes or spaces. Maria Lopez, finance clerk at the City of Fresno Public Works, enters 123456789 in this box.
If your account number is fewer than 9 digits because it is an older legacy account, left-pad with zeros so the field is filled. Filing without an account number is the single fastest way to get your return mailed back unprocessed, costing you the entire 30-day grace window before the 10% penalty hits. A common misconception is that the federal EIN is acceptable here; it is not, and substituting it routes your payment to a non-existent account.
Header: Reporting Period
The reporting period asks which calendar quarter the return covers. Write the start and end dates in MM/DD/YYYY format, such as 01/01/2026 through 03/31/2026 for the first quarter of 2026. Carlos Nguyen, accountant for the Los Angeles County Transit District, enters 04/01/2026 through 06/30/2026 on his Q2 return.
If your agency is on a fiscal-year reporting cycle internally, ignore that and use the calendar quarter. The CDTFA computes the due date from the calendar quarter, so a fiscal-year date guarantees a late-filing notice. Filers often think the reporting period is the date they prepare the return; it is not, and this confusion causes about 8% of late-filing notices according to CDTFA stakeholder data.
Header: Owner’s Name and Business Name
Enter the legal name of the government entity exactly as it appears on the license. For the City of Fresno Public Works Department, write CITY OF FRESNO in the owner field and PUBLIC WORKS DEPARTMENT in the business name field.
If your agency operates under a “doing business as” name (e.g., a transit district branded as “Metro”), use the legal name on top and the DBA in the business-name slot. A mismatch between the name on the return and the name on the license triggers a manual review and adds 10–14 days of processing. Many filers think the field accepts abbreviations such as “LA County”; the CDTFA matching engine rejects abbreviations and the return goes to the exception queue.
Line 1: Total Gallons of Tax-Paid Diesel Fuel Removed, Entered, or Sold
Line 1 asks for the total gallons of diesel fuel on which the California excise tax was paid that your agency removed from a terminal, entered into California, or sold during the quarter. Enter the figure in whole gallons, rounded to the nearest gallon. Maria enters 14,250 gallons for Q1 because the City of Fresno’s supplier delivered 14,250 tax-paid gallons that quarter.
If you received fuel from multiple suppliers, sum them and enter the total. The number must reconcile to the bills of lading you keep under RTC §60401. The biggest mistake on Line 1 is entering only the gallons you sold; the line wants every tax-paid gallon that moved, including gallons your agency burned itself, and missing this understates the base for the credit on Line 5. A common misconception is that dyed (off-road) gallons belong on Line 1; they do not, and including them inflates your taxable base.
Line 2: Total Gallons of Ex-Tax Diesel Fuel Removed, Entered, or Sold
Line 2 captures gallons of diesel fuel where tax has not yet been paid but is now due because your agency removed, entered, or sold them. Enter whole gallons. Carlos enters 3,800 gallons because the Transit District drew that much clear diesel ex-tax from its supplier and used it on California highways.
The gallons on Line 2 are the heart of the return because tax is owed on them at $0.41 each. If you carry inventory from quarter to quarter, only the gallons that moved out this quarter belong here. Entering opening inventory on Line 2 double-counts gallons and creates a credit-tracking nightmare. Many filers think gallons sold to another government entity are exempt and can be left off Line 2; they must be included on Line 2 and then offset on Line 4, not omitted.
Line 3: Total (Line 1 + Line 2)
Line 3 is the arithmetic sum of Lines 1 and 2. Add them and enter the total in whole gallons. Maria writes 14,250 + 0 = 14,250; Carlos writes 0 + 3,800 = 3,800.
This line drives the entire computation, so a typo here cascades through the rest of the return. The portal does the math automatically, but on paper you must double-check. The single most common Line 3 error is transposing digits (e.g., 14,520 instead of 14,250), and the CDTFA will use whichever number you wrote, even if it overstates your tax. Filers sometimes believe Line 3 should equal physical inventory; it should not, because it is a flow figure, not a balance.
Line 4: Total Gallons of Ex-Tax Sales to U.S. Government and Other Exempt Users
Line 4 reduces your taxable base by the gallons you sold ex-tax to the U.S. government, to another licensed government entity, or to a use exempt under RTC §60100. Enter whole gallons. Janet Park, fuel coordinator for the San Diego Unified School District, enters 1,200 gallons sold to a neighboring school district’s bus fleet.
You must keep an exemption certificate on file from each buyer for every gallon claimed on Line 4. Without the certificate, the CDTFA disallows the deduction on audit and assesses tax plus the 10% penalty on the disallowed gallons. Filers often confuse “exempt user” with “nonprofit”; nonprofits are not automatically exempt from diesel fuel tax, and treating a nonprofit sale as exempt is one of the top three audit findings in CDTFA stakeholder reports.
Line 5: Net Taxable Gallons (Line 3 minus Line 4)
Line 5 is the taxable-gallon figure that drives the tax due. Subtract Line 4 from Line 3 and enter the result. Maria writes 14,250 − 0 = 14,250; Janet writes 9,400 − 1,200 = 8,200.
If Line 5 comes out negative, you stop and call the CDTFA Motor Carrier Office before filing because a negative number means a credit situation that the form cannot accept directly. Filing a negative Line 5 freezes your account in the portal. A common misconception is that you can carry a negative figure forward as a credit on the next return; you cannot, and you must instead file a refund claim on CDTFA-770-DU.
Line 6: Tax Rate
Line 6 is the per-gallon excise tax rate in effect during the reporting quarter. The rate adjusts every July 1 under RTC §60050. For periods July 1, 2025 through June 30, 2026, enter $0.41 per gallon as published on the CDTFA Tax Rates page.
If your reporting quarter straddles July 1 (it should not, since quarters end June 30 and September 30), you must split the gallons across two returns at the old and new rates. Using last year’s rate is a common error and causes a recomputation notice within 30 days. Many filers think Line 6 is editable; it is not, and writing in a different rate triggers a manual review.
Line 7: Total Tax (Line 5 × Line 6)
Multiply Line 5 by Line 6 and enter the result in dollars and cents. Maria writes 14,250 × $0.41 = $5,842.50; Janet writes 8,200 × $0.41 = $3,362.00.
Round to the nearest cent. The portal computes Line 7 automatically; on paper, double-check the multiplication because the CDTFA does not “fix” your math in your favor — they bill you for any underpayment plus interest. The most common Line 7 mistake is using the wrong rate from a prior year, which is why locking in the rate from the CDTFA Tax Rates page before computing matters. Some filers think they can round to the nearest dollar; they cannot, and rounding errors above $1.00 trigger a math-error notice.
Line 8: Less: Tax Prepayment
Line 8 captures any prepayment your agency made to a supplier or directly to the CDTFA under RTC §60201. Enter the dollar amount. Carlos enters $1,558.00 because the Transit District prepaid two months of estimated tax in May.
You must attach the prepayment receipt or credit memo number to support Line 8 on audit. Claiming a prepayment that does not match the CDTFA’s records causes a billing for the disputed amount plus interest. Filers sometimes think the supplier’s invoice line for “diesel fuel tax” counts as a prepayment; it does not unless the supplier remitted it under your account, and confirming that takes a quick call to the supplier’s tax desk.
Line 9: Net Tax Due (Line 7 minus Line 8)
Line 9 is your net tax for the quarter. Subtract Line 8 from Line 7. Carlos writes $1,558.00 − $1,558.00 = $0.00; Maria writes $5,842.50 − $0.00 = $5,842.50.
If Line 9 is zero, you still file the return; do not skip it. A negative Line 9 means a refund situation, and you should file CDTFA-770-DU instead of forcing a negative on this return. The most common Line 9 mistake is leaving it blank when zero is due, which the CDTFA reads as “return incomplete” and assesses the $50 minimum penalty.
Line 10: Penalty
Line 10 is the late-filing or late-payment penalty, 10% of Line 9 under RTC §60250. If you are filing on time, enter $0.00. If you are filing late, multiply Line 9 by 0.10 and enter the result.
For example, Maria files Q1 on May 15, two weeks late; she enters $5,842.50 × 0.10 = $584.25. The penalty is automatic; the CDTFA does not waive it without a written request showing reasonable cause under Regulation 1703. A common misconception is that the penalty is prorated by days late; it is not — one day late is the same 10% as 30 days late.
Line 11: Interest
Line 11 is interest on any unpaid tax, computed monthly at the CDTFA’s published interest rate. For the 2026 first half, the rate is 9% annual, or 0.0075 per month. Multiply Line 9 by 0.0075 for each full or partial month late.
Maria, two weeks late, enters $5,842.50 × 0.0075 = $43.82 for one partial month. Interest accrues from the original due date until the date of payment, not the date of filing. Filers often think interest stops when they mail the return; it does not, and underestimating interest by even a dollar leaves the account open and accruing.
Line 12: Total Amount Due (Lines 9 + 10 + 11)
Line 12 is the grand total your agency owes for the quarter. Add Lines 9, 10, and 11. Maria writes $5,842.50 + $584.25 + $43.82 = $6,470.57; Carlos writes $0.00 + $0.00 + $0.00 = $0.00.
Pay this exact amount; underpayment by even one cent leaves the account open and continues to accrue interest. The most common Line 12 error is paying Line 9 only and forgetting penalty and interest, which keeps the account in delinquent status. A misconception is that paying online lets you skip Line 12 because the portal computes it; you should still verify the total before submitting.
Schedule A: Detail of Ex-Tax Sales
Schedule A backs up the gallons claimed on Line 4. For every ex-tax sale, list the buyer’s name, address, date, invoice number, and gallons. Janet lists Imperial Beach Unified, 800 Imperial Beach Blvd, Imperial Beach CA, 03/14/2026, INV-4421, 1,200 gallons.
Schedule A must reconcile to Line 4 to the gallon. A 1-gallon mismatch is enough to trigger a math-error notice. The CDTFA can ask for the underlying exemption certificate within 30 days under RTC §60401, so keep them filed by invoice number. Filers often think Schedule A is optional if Line 4 is small; it is not, and any non-zero Line 4 without a matching Schedule A draws an audit letter.
Signature Block
The signature block requires the printed name, title, telephone number, signature, and date of an authorized signer. Maria Lopez signs as Finance Clerk, City of Fresno, (559) 555-1234, 04/28/2026.
The signer must hold written delegation from the governing body, kept in your agency’s permanent file. An unauthorized signature voids the return under RTC §60205. A common mistake is having the preparer sign instead of an authorized officer; the CDTFA accepts the return but will not honor representations made on it during audit. Many filers think a digital signature is invalid; it is valid in the portal, but a typed name on a paper return is not.
Three Filled-Out Examples Using Real Scenarios
Below are three full walkthroughs of named filers from California government entities, each completing CDTFA-501-DG for a single quarter.
Scenario 1: City of Fresno Public Works (Maria Lopez, Q1 2026)
The City sells small amounts of clear diesel to a paving contractor working a city street project, and uses the rest for its own fleet on California highways.
| Form Section | What Maria Enters |
|---|---|
| Account Number | 123456789 |
| Reporting Period | 01/01/2026 – 03/31/2026 |
| Owner / Business Name | CITY OF FRESNO / PUBLIC WORKS DEPARTMENT |
| Line 1 (tax-paid gallons) | 14,250 |
| Line 2 (ex-tax gallons) | 0 |
| Line 4 (exempt sales) | 0 |
| Line 5 (taxable gallons) | 14,250 |
| Line 7 (tax at $0.41) | $5,842.50 |
| Line 12 (total due) | $5,842.50 |
| Signature | Maria Lopez, Finance Clerk, 04/28/2026 |
Scenario 2: Los Angeles County Transit District (Carlos Nguyen, Q2 2026)
The District buys clear diesel ex-tax to fuel its own bus fleet, prepays estimated tax monthly, and makes no outside sales.
| Form Section | What Carlos Enters |
|---|---|
| Account Number | 234567891 |
| Reporting Period | 04/01/2026 – 06/30/2026 |
| Owner / Business Name | LOS ANGELES COUNTY TRANSIT DISTRICT |
| Line 1 (tax-paid gallons) | 0 |
| Line 2 (ex-tax gallons) | 3,800 |
| Line 5 (taxable gallons) | 3,800 |
| Line 7 (tax at $0.41) | $1,558.00 |
| Line 8 (prepayment) | $1,558.00 |
| Line 9 (net tax due) | $0.00 |
| Line 12 (total due) | $0.00 |
| Signature | Carlos Nguyen, Senior Accountant, 07/20/2026 |
Scenario 3: San Diego Unified School District (Janet Park, Q3 2026)
The District fuels its own buses, sells surplus to a neighboring school district, and pays tax on a small remainder used on California highways for non-bus vehicles.
| Form Section | What Janet Enters |
|---|---|
| Account Number | 345678912 |
| Reporting Period | 07/01/2026 – 09/30/2026 |
| Owner / Business Name | SAN DIEGO UNIFIED SCHOOL DISTRICT |
| Line 1 (tax-paid gallons) | 0 |
| Line 2 (ex-tax gallons) | 9,400 |
| Line 4 (exempt sales) | 1,200 |
| Line 5 (taxable gallons) | 8,200 |
| Line 7 (tax at $0.41) | $3,362.00 |
| Line 9 (net tax due) | $3,362.00 |
| Schedule A | Imperial Beach Unified, 800 Imperial Beach Blvd, Imperial Beach CA, 09/14/2026, INV-4421, 1,200 gallons |
| Signature | Janet Park, Fuel Coordinator, 10/25/2026 |
How to File the Completed Form
The return is due the last day of the month following the close of each quarter. Q1 is due April 30, Q2 is due July 31, Q3 is due October 31, and Q4 is due January 31. Late filing draws the 10% penalty under RTC §60250 plus interest from the CDTFA interest rate page.
Online filing. Log in to the CDTFA online services portal, select File a Return under your Government Entity Diesel Fuel account, enter Lines 1–12 (Schedule A is uploaded as a CSV), and pay by ACH debit using your bank routing and account number. There is no fee. Processing is real-time, and the portal emails a filing confirmation within minutes that you should print and save as proof of filing.
Mail filing (waiver required). Send the signed paper return and a check payable to California Department of Tax and Fee Administration to CDTFA, PO Box 942879, Sacramento, CA 94279-0001. The check must include your account number in the memo line. Allow 10–15 business days for processing. Always send by certified mail with return receipt as proof of filing because the postmark controls the timeliness determination under Regulation 1702.
EFT filing. Agencies with prior-year liability over $20,000 must pay by EFT under RTC §60252. Initiate the ACH credit through your bank using the CDTFA’s EFT instructions at least one business day before the due date. The trace number from your bank is your proof of payment.
In-person filing. You may file at any CDTFA field office during business hours. Bring two copies so one can be date-stamped and returned to you as proof.
What Happens After You File
After the CDTFA accepts your return, you receive a confirmation number (electronic) or a stamped copy (in person) within 1–3 business days. The agency posts your payment to your account within 5 business days for ACH debit and 7–10 business days for paper checks.
If your math reconciles and Schedule A balances to Line 4, the return moves to closed status and no further action is required. If the agency finds a math error, they mail a Notice of Determination under RTC §60302 within 60 days; you have 30 days to pay or petition for redetermination.
The CDTFA may select your return for audit, especially if Line 4 exceeds 20% of Line 3 or if your gallons swing more than 25% quarter-over-quarter. An audit letter requests bills of lading, exemption certificates, and Schedule A backup within 30 days. Cooperating fully and producing clean records typically closes the audit in 60–90 days with no change.
Keep every return and supporting record for at least four years from the filing date under RTC §60401. Some agencies extend this to seven years to align with their internal record-retention schedule, which is a smart practice.
Mistakes to Avoid When Filling Out the Form
- Filing under the wrong reporting period. This posts your payment to the wrong quarter and triggers a late-filing notice on the correct quarter, doubling your penalty exposure.
- Leaving Line 9 blank when zero is due. The CDTFA treats a blank Line 9 as an incomplete return and assesses the $50 minimum penalty.
- Using last year’s tax rate on Line 6. The rate adjusts every July 1, and using the old rate causes a recomputation notice plus interest on the shortfall.
- Including dyed (off-road) diesel on Line 1 or Line 2. Dyed diesel is not subject to this tax and inflates your taxable base, costing you real tax dollars.
- Skipping Schedule A when Line 4 is non-zero. A non-zero Line 4 without matching Schedule A draws an audit letter within 90 days.
- Forgetting to keep exemption certificates. Without certificates, Line 4 deductions are disallowed on audit, and tax plus 10% penalty hits the disallowed gallons.
- Treating a nonprofit sale as exempt. Nonprofits are not automatically exempt from diesel fuel tax, and this is a top-three audit finding.
- Letting an unauthorized employee sign. The return is voidable, and representations made on it are not binding on the CDTFA during audit.
- Mailing a paper return without a filing waiver. The return is treated as not filed, and the 10% penalty applies to any tax due.
- Underpaying penalty or interest. Even a one-cent shortfall keeps the account open and accruing additional interest each month.
- Transposing digits on Line 3. The CDTFA uses the number you wrote, even if it overstates your tax, and getting a refund later requires a separate claim on CDTFA-770-DU.
Do’s and Don’ts
- Do download a fresh copy of Form CDTFA-501-DG every quarter, because the rate and revision date change.
- Do file electronically through the CDTFA online services portal, because the portal catches arithmetic errors before submission.
- Do reconcile Schedule A to Line 4 to the gallon, because any mismatch triggers a math-error notice.
- Do keep bills of lading and exemption certificates for at least four years, because the CDTFA can request them under RTC §60401.
- Do file a zero return when no tax is due, because failing to file draws the same $50 minimum penalty as failing to pay.
- Do verify the signer holds written delegation from the governing body, because an unauthorized signature voids the return.
- Don’t include dyed-diesel gallons on Line 1 or Line 2, because they are not subject to this tax.
- Don’t use last year’s rate on Line 6, because the rate adjusts every July 1 under RTC §60050.
- Don’t carry a negative Line 9 forward, because credits must be claimed on CDTFA-770-DU.
- Don’t mail a paper return without an active filing waiver, because the return is treated as not filed.
- Don’t abbreviate the agency name, because the CDTFA matching engine rejects abbreviations and routes the return to an exception queue.
- Don’t rely on the supplier’s invoice line for “diesel fuel tax” as a Line 8 prepayment, because it counts only if the supplier remitted it under your account.
Pros and Cons of Filing on Your Own vs. With Help
Filing in-house works for most government entities because the form is short and the CDTFA portal handles the math. Hiring a fuel-tax consultant or contracting with another agency makes sense when transaction volume is high, when audits are looming, or when staff turnover has wiped out institutional knowledge.
Pros of filing on your own:
- No outside fee, which matters for small districts on tight budgets.
- Faster turnaround because there is no handoff to a third party.
- Direct knowledge of the agency’s fuel operations, which speeds Schedule A preparation.
- Stronger institutional memory for future quarters and audits.
- Full control of the filing calendar and proof-of-filing records.
Cons of filing on your own:
- Risk of arithmetic errors that draw math-error notices and interest.
- Higher chance of missing rate-change dates and using the wrong Line 6 figure.
- Staff turnover can break filing continuity and create late returns.
- No professional shield in an audit, so the agency bears all interpretation risk.
- Time cost for finance staff who already wear many hats.
CDTFA-501-DG vs. Adjacent California Diesel Forms
| Form | When to Use It |
|---|---|
| CDTFA-501-DG | Quarterly excise tax return for licensed California government entities reporting diesel use and sales |
| CDTFA-501-DD | Diesel fuel claim for refund by ultimate purchaser of tax-paid fuel used for an exempt purpose |
| CDTFA-501-DI | Quarterly diesel fuel tax return for exempt bus operators and interstate users (not government entities) |
| CDTFA-770-DU | Refund claim for tax-paid diesel used in a nontaxable manner, filed outside the quarterly cycle |
| CDTFA-501-DB | Supplier of diesel fuel tax return, used by licensed suppliers, not government entities |
FAQs
Do I file CDTFA-501-DG if my agency had no diesel activity this quarter?
Yes. A zero return is required under RTC §60205. Skipping it draws the same $50 minimum late-filing penalty as a return with tax due.
Can my federal EIN go in the account-number header instead of the CDTFA number?
No. Only the 9-digit CDTFA-issued account number is accepted, and substituting the EIN routes your payment to a non-existent account.
Does dyed (off-road) diesel go on Line 1 or Line 2?
No. Dyed diesel is not subject to the diesel fuel excise tax, and including it on Line 1 or Line 2 inflates your taxable base.
Are sales to nonprofits exempt on Line 4?
No. Nonprofits are not automatically exempt from diesel fuel tax, and treating such a sale as exempt is one of the top three audit findings.
Should I round dollar amounts to the nearest dollar on Line 7?
No. Round to the nearest cent. Rounding errors above $1.00 trigger a math-error notice from the CDTFA.
Do I write the supplier’s “diesel fuel tax” invoice line as a prepayment on Line 8?
No. It counts only if the supplier remitted the tax under your account. Confirm with the supplier’s tax desk before claiming it.
Can I carry a negative Line 9 forward to next quarter?
No. Credits must be claimed on CDTFA-770-DU as a refund claim, not netted on the next CDTFA-501-DG.
Is a digital signature valid on the return?
Yes, when filed through the CDTFA online services portal. On a paper return, a typed name without a wet signature is not accepted.
Does the 10% penalty get prorated if I’m only one day late?
No. The penalty under RTC §60250 is a flat 10% whether you are one day or 30 days late.
Can I file CDTFA-501-DG by email?
No. The CDTFA accepts the return through the online portal, by mail with a filing waiver, or in person at a field office — never by email.
Do I need a Schedule A if Line 4 is only a few gallons?
Yes. Any non-zero Line 4 requires a matching Schedule A, and a missing schedule draws an audit letter within 90 days.
Is the $0.41 rate on Line 6 the same all year?
No. The rate adjusts every July 1 under RTC §60050. Always verify the current figure on the CDTFA Tax Rates page before filing.
Can the preparer sign in the signature block instead of an officer?
No. The signer must hold written delegation from the governing body, and a preparer signature voids representations on the return during audit.
Do I keep records for three years like federal IRS rules?
No. California requires at least four years from the filing date under RTC §60401, and many agencies keep them seven.
Related reading
- How to Fill Out California Form CDTFA-501-AB (w/Examples) + FAQs
- How to Fill Out California Form CDTFA-501-MV (w/Examples) + FAQs
- How to Fill Out California Form CDTFA-501-PS (w/Examples) + FAQs
- How to Fill Out California Form CDTFA-501-EJ (w/Examples) + FAQs
- How to Fill Out California Form CDTFA-501-DD (w/Examples) + FAQs
- How to Fill Out California Form CDTFA-770 (w/Examples) + FAQs