Yes, you can update a W-4 in Gusto in minutes, either as an employee through your self-service profile or as an admin through the employee’s tax setup page. The update flows to the next payroll run once it is saved before the payroll deadline, and it changes how much federal income tax comes out of each paycheck going forward.
The rule that sits behind this feature is the federal withholding system under IRC §3402, which forces every employer to withhold income tax from wages based on the employee’s most recent valid Form W-4. Under Treas. Reg. §31.3402(f)(2)-1, the employee must give the employer a signed W-4, and the employer must start using a new W-4 no later than the start of the first payroll period ending on or after the 30th day from the date received. If the withholding is wrong, the employer can face liability under IRC §3403 and the employee can owe penalties under IRC §6682 for a false certificate.
According to the IRS Data Book for Fiscal Year 2024, more than 256 million federal tax returns and related forms were processed, and the agency’s own Tax Withholding Estimator page reminds workers that roughly two-thirds of filers get a refund every year, which is a strong sign that most W-4s are not tuned well. A properly updated W-4 inside Gusto fixes that gap fast.
- 📝 Exact click-by-click steps to update a federal W-4 inside Gusto, both as an employee and as an admin
- 🧾 How state withholding certificates like the California DE-4, New York IT-2104, and Illinois IL-W-4 flow through Gusto
- 👨👩👧 Five named real-world scenarios covering marriage, dual income, dependents, side gigs, and rehires
- ⚠️ The biggest W-4 mistakes that trigger under-withholding, IRS lock-in letters, and surprise April tax bills
- 📊 Pros, cons, do’s, don’ts, and a plain-English walk-through of every single line on the current Form W-4
What a W-4 Actually Does Inside Gusto
The Form W-4, officially called the Employee’s Withholding Certificate, tells your employer how much federal income tax to pull from each paycheck. Gusto takes the numbers you enter on the form and plugs them into the percentage method tables published each year in IRS Publication 15-T. The result is the federal income tax line you see on your Gusto pay stub.
Gusto does not make up its own withholding rules. It follows the post-2020 redesigned W-4, which removed personal allowances and replaced them with dollar-based inputs for dependents, other income, deductions, and extra withholding. That redesign came out of the Tax Cuts and Jobs Act of 2017, which suspended personal exemptions through 2025 and forced the IRS to rebuild the form.
The consequence of ignoring your W-4 is simple and painful. If your W-4 is stale, the default in Gusto is the old information on file, which might still say Single, no adjustments from the day you were hired. A married parent of two who never updated that default can easily over-withhold by $3,000 to $5,000 a year, which is an interest-free loan to the U.S. Treasury.
A common misconception is that the W-4 controls your total tax bill. It does not. Your actual tax is set by your Form 1040 at year end. The W-4 only controls the pace of prepayment through payroll.
The Legal Duty to File a W-4
Every new hire must hand in a signed W-4 on or before their first day, per Treas. Reg. §31.3402(f)(5)-1. If the employee refuses, Gusto and the IRS both treat the worker as Single with no adjustments, which almost always over-withholds. That rule exists so the Treasury collects tax throughout the year rather than in one April lump.
The consequence of skipping this step is a bigger paycheck deduction than needed and a larger refund the following spring. A real-world example is Sofia, a barista at a coffee shop using Gusto who never submitted a W-4 during onboarding. Her employer defaulted her to Single, and she discovered in February that she had overpaid by $2,400 because she qualified as Head of Household with one child.
A common misconception is that you can write exempt on the form to stop all withholding. You can only claim exempt if you had no tax liability last year and expect none this year, per the instructions on Form W-4 page 2. A false exempt claim can trigger a $500 civil penalty under IRC §6682.
When You Must Update a W-4
You are not required by law to update your W-4 every year, but the IRS strongly urges a fresh one after any life or money event, per IRS Publication 505. Marriage, divorce, a new baby, a second job, a working spouse, a large bonus, or a home purchase all change the right withholding number. Waiting until tax time means a bill plus possible underpayment penalty under IRC §6654.
The consequence of waiting is cash you do not have in April. A real-world example is Derek, a software engineer who started a $30,000 per year side gig in March but did not update his Gusto W-4. He owed $6,200 plus a $180 underpayment penalty the next April because payroll kept withholding as if his day job was his only income.
A common misconception is that you only need to update the W-4 at year end. You can update it any time during the year, and Gusto will prorate withholding on the next run so the rest of the year catches up.
How to Update a Federal W-4 in Gusto as an Employee
Employees update their own W-4 inside the Gusto employee portal, which is the fastest path. You never need to print, sign, and mail anything, because Gusto stores a digital signature that satisfies IRS Publication 1167 rules on electronic substitutes. The change takes effect on the very next payroll, as long as you save it before your company’s payroll cutoff, which is usually two business days before payday.
Step one is to log in at app.gusto.com using your work email and password. Step two is to click your profile icon in the top right, then choose Profile from the drop-down. Step three is to select the Job & Pay tab on the left sidebar. Step four is to scroll to the Taxes section and click Edit next to Federal Tax Withholdings (Form W-4).
Step five is to work through the on-screen wizard, which mirrors the paper Form W-4 step by step. You pick your filing status, answer the multiple-jobs question, enter dependent credits, add any other income or deductions, and type any extra per-paycheck withholding. Step six is to electronically sign and click Save. Gusto emails you a PDF copy for your records.
Filing Status in Step 1(c)
Your filing status is the single biggest driver of withholding. The three choices on the form are Single or Married filing separately, Married filing jointly or Qualifying surviving spouse, and Head of household. Each one pulls a different standard deduction and bracket table from Publication 15-T, and the wrong box can swing your paycheck by hundreds of dollars.
The consequence of picking the wrong status is either too much or too little tax taken out. A real-world example is Maria, a nurse who married in June but kept Single on her Gusto W-4 through December. She over-withheld by about $2,800 because the Married Filing Jointly brackets are wider and the standard deduction is double.
A common misconception is that you must match your W-4 status to the status you plan to use on your Form 1040. You do not. You can pick any status that lowers or raises withholding to your target, though matching is usually simplest.
Multiple Jobs in Step 2
Step 2 is for workers who hold more than one job or who are married with a working spouse. Gusto offers three ways to handle this, and each one maps to a boxed option on the paper form. Option (a) is the online IRS Tax Withholding Estimator, option (b) is the Multiple Jobs Worksheet on page 3 of the W-4, and option (c) is a simple checkbox for two similar-pay jobs.
The consequence of skipping Step 2 with two jobs is severe under-withholding, because each employer assumes its paycheck is your only income and applies the full standard deduction. A real-world example is Jamal, an accountant whose wife Aisha earns a similar salary. They each checked box 2(c) in Gusto, which cut the standard deduction in half for withholding and stopped a projected $4,900 April tax bill.
A common misconception is that option (c) works for mismatched salaries. It does not. If one job pays much more than the other, use option (a) or option (b) for accuracy.
Dependents in Step 3
Step 3 is where you convert the Child Tax Credit and the Credit for Other Dependents into a withholding cut. Multiply qualifying children under 17 by $2,000, multiply other dependents by $500, add them together, and type the total into the dollar box. The credit amounts come from IRC §24 as amended by the Tax Cuts and Jobs Act.
The consequence of skipping Step 3 is over-withholding by $167 per month per child. A real-world example is Priya, a project manager with three kids under 17 who entered $6,000 in Gusto’s Step 3 box. Her paycheck jumped by about $500 per month, money she rerouted to a 529 plan.
A common misconception is that only your biological children count. Stepchildren, foster children, and qualifying relatives can also count under the dependent tests in IRS Publication 501.
Other Adjustments in Step 4
Step 4 has three optional boxes. Box 4(a) is other income not from jobs, such as interest, dividends, or self-employment income. Box 4(b) is deductions above the standard deduction, which most filers leave blank. Box 4(c) is extra withholding per paycheck, which is the single most precise lever on the form.
The consequence of ignoring Step 4 when you have side income is a surprise bill. A real-world example is Derek from earlier, who added $250 per paycheck in box 4(c) after starting his side gig. That $6,500 annual bump covered his extra income tax plus self-employment tax.
A common misconception is that box 4(c) money goes into a separate account. It does not. The extra dollars go straight to the IRS and show up on your Form W-2 box 2 at year end just like regular withholding.
How to Update a W-4 in Gusto as an Admin
Admins can update a team member’s W-4 on that person’s behalf, which is useful when an employee sends a signed paper W-4 or when a lock-in letter arrives from the IRS. The steps live under the People section of the Gusto admin dashboard. Any admin edit still creates an audit log entry with the editor’s name and timestamp, which protects the company under Treas. Reg. §31.3402(f)(2)-1.
Step one is to sign in at app.gusto.com with admin credentials. Step two is to click People and then Team Members. Step three is to click the employee’s name, then open the Job & Pay tab and scroll to Tax Setup. Step four is to click Edit next to Federal Tax Withholdings, mirror the employee’s signed paper W-4 line for line, and save.
Admins cannot forge a signature. Gusto records that the change was made by the admin, not the employee, which is why best practice is to keep the physical or scanned W-4 in the employee’s digital file for at least four years, per IRS recordkeeping rules in Publication 583.
Handling IRS Lock-In Letters
If the IRS decides an employee is under-withholding, it sends the employer a Letter 2800C, also called a lock-in letter. The letter tells the employer the exact filing status and withholding to use, and the employer must follow it within 60 days. Gusto supports lock-in letters through a dedicated admin flow.
The consequence of ignoring a 2800C is that the employer becomes personally liable for the under-withheld tax under IRC §3403. A real-world example is a small bakery that filed a 2800C away in a drawer and eventually owed $14,000 in unpaid tax plus interest when the IRS audited two years later.
A common misconception is that the employee can override the letter by submitting a new W-4 in Gusto. They cannot. The employer must keep using the locked-in numbers until the IRS sends a Letter 2808C releasing the lock.
Handling Rehires and Status Changes
A rehired employee needs a new W-4 if there has been a break in service of more than 12 months, per the IRS rehire rules. Admins reopen the terminated profile in Gusto, click Rehire, and the W-4 wizard triggers again. Mid-year status changes, such as an employee getting married, should be employee-driven, but an admin can enter them with a signed paper form.
The consequence of skipping the rehire W-4 is using stale data that might be years old. A real-world example is Sofia, rehired after 14 months away, whose admin forgot to rerun the W-4 step. Her old Single, no dependents record kept running, and she over-withheld by $1,900 before catching it in October.
A common misconception is that a verbal update is enough. It is not. Treas. Reg. §31.3402(f)(2)-1 requires a signed writing, whether paper or electronic.
State Withholding Certificates in Gusto
Gusto also handles state income tax withholding, and most states require a separate state certificate on top of the federal W-4. Nine states have no wage income tax at all, including Texas, Florida, and Washington, so employees there skip the state step entirely. For the other 41 states plus D.C., the state form lives in the same Taxes area as the federal W-4.
California uses Form DE-4, which looks similar to the federal form but still uses allowances. New York uses Form IT-2104, which is unusually detailed and asks about New York City residency. Illinois uses Form IL-W-4, which is short and allowance-based.
The consequence of relying only on the federal W-4 in a state that requires its own form is state under- or over-withholding. A common misconception is that the federal W-4 automatically controls state withholding inside Gusto. It does not. You must update each state form separately.
Form W-4 Line-by-Line Walk-Through
The current Form W-4 has five steps plus a signature block, and Gusto mirrors all of them. Step 1 captures name, address, Social Security number, and filing status. Step 2 addresses multiple jobs. Step 3 claims dependents. Step 4 lists other adjustments. Step 5 is the signature, which is legally required under Treas. Reg. §31.3402(f)(2)-1.
Every box interacts with every other box through the withholding formula in Publication 15-T. Changing one line can move the paycheck by a meaningful amount, so review every answer before saving in Gusto.
| Form W-4 Line | What It Controls |
|---|---|
| Step 1(a) Name and address | Identity and state tax jurisdiction for payroll |
| Step 1(b) Social Security number | Matches IRS records to prevent CP2100 mismatch notices |
| Step 1(c) Filing status | Selects the standard deduction and bracket table used by Gusto |
| Step 2(c) Two similar jobs checkbox | Cuts the standard deduction in half for each job |
| Step 3 Dependents dollars | Lowers annual withholding dollar-for-dollar |
| Step 4(a) Other income | Raises withholding to cover non-wage income |
| Step 4(b) Deductions | Lowers withholding if you itemize above the standard deduction |
| Step 4(c) Extra per-paycheck | Adds a flat dollar amount to every paycheck’s federal tax |
| Step 5 Signature | Legally validates the form under Treas. Reg. §31.3402(f)(2)-1 |
Three Popular W-4 Update Scenarios
Every W-4 update falls into a pattern. The three below cover the vast majority of Gusto W-4 edits, and each shows the trigger and the payroll result.
Scenario 1: New Baby Arrives
| Life Event | Gusto W-4 Action and Paycheck Result |
|---|---|
| Employee has a baby in March | Log in, open Step 3, add $2,000 for one qualifying child, save before next payroll cutoff |
| Filing status stays the same | Paycheck grows by roughly $167 per month from the next run |
| No paper form required | Electronic signature satisfies IRS e-sign rules in Publication 1167 |
Scenario 2: Spouse Starts Working
| Life Event | Gusto W-4 Action and Paycheck Result |
|---|---|
| Non-working spouse takes a new job at similar pay | Both spouses log into their own Gusto accounts and check Step 2(c) |
| Filing status stays Married Filing Jointly | Each paycheck drops as standard deduction splits across two jobs |
| Avoids a projected $4,900 April bill | Matches Publication 15-T dual-income tables |
Scenario 3: Side Gig Starts Paying
| Life Event | Gusto W-4 Action and Paycheck Result |
|---|---|
| Employee launches a 1099 consulting side gig | Open Step 4(c), add an extra per-paycheck dollar amount |
| Or use Step 4(a) for projected non-wage income | Covers both income tax and self-employment tax |
| Avoids underpayment penalty under IRC §6654 | Penalty is skipped if withholding covers 90% of current tax or 100% of prior-year tax |
Named Real-World Examples
Maria is a hospital nurse in Dallas earning $78,000. She married Luis in June, logged into Gusto the next week, switched Step 1(c) from Single to Married Filing Jointly, and signed. Her next paycheck rose by $190 because the wider MFJ brackets in Publication 15-T kicked in immediately.
Jamal is a senior accountant in Chicago earning $110,000. His wife Aisha earns $115,000 at a separate employer. Both checked box 2(c) in their Gusto accounts, which cut each paycheck by about $95 but avoided a projected $4,900 April bill plus a $140 underpayment penalty under IRC §6654.
Priya is a project manager in Atlanta with three children under 17. She entered $6,000 in Step 3 of her Gusto W-4, which lifted her net paycheck by about $500 per month. That matches the Child Tax Credit formula in IRC §24.
Derek is a software engineer in Austin with a $30,000 per year Etsy side gig. He added $250 per paycheck in Step 4(c) of Gusto, generating $6,500 of extra withholding to cover federal income tax plus self-employment tax under IRC §1401.
Sofia is a barista rehired at the same café after a 14-month break. Her admin rehired her in Gusto, triggered the W-4 wizard, and Sofia switched her status to Head of Household with one dependent. Her withholding dropped by $215 per month.
Mistakes to Avoid When Updating a W-4 in Gusto
A W-4 is short, but the traps are real. Any of these errors can cause surprise bills, IRS notices, or even lock-in letters.
- Claiming exempt without meeting both tests in the Form W-4 instructions can trigger a $500 penalty under IRC §6682.
- Forgetting to check box 2(c) in a two-earner household causes under-withholding of $2,000 to $6,000 per year.
- Entering dependent credits in Step 3 when someone else claims the child causes under-withholding and a likely IRS math-error notice under IRC §6213(b).
- Using the federal W-4 alone in states like California or New York leaves state withholding at default Single, zero, usually over-withholding.
- Saving the W-4 in Gusto after the payroll cutoff pushes the change to the following payroll, not the next one.
- Ignoring a Letter 2800C lock-in letter exposes the employer to personal liability under IRC §3403.
- Leaving a stale W-4 after a divorce keeps the wider MFJ brackets running, which leads to a huge April bill plus a possible underpayment penalty under IRC §6654.
- Skipping Step 4(a) when you have big dividend or interest income causes a shortfall that Gusto cannot predict.
- Using the Multiple Jobs Worksheet with wildly wrong estimates, rather than the IRS Tax Withholding Estimator, can swing withholding by thousands.
- Failing to sign Step 5 voids the form under Treas. Reg. §31.3402(f)(2)-1, and Gusto will revert to default Single, no adjustments.
Do’s and Don’ts
- Do run the IRS Tax Withholding Estimator first, because it produces the exact Step 4(c) dollar amount you need.
- Do update your W-4 in Gusto right after any life event, because the IRS tells you to in Publication 505.
- Do keep a downloaded PDF of the signed W-4 for four years, matching Publication 583 recordkeeping rules.
- Do also update the state withholding certificate, such as the DE-4 or IT-2104.
- Do recheck withholding every January, because the Publication 15-T tables change each year.
- Don’t claim exempt unless you truly had zero tax last year and expect zero this year.
- Don’t guess at Step 3 dependent dollars, because the math is exact at $2,000 per child and $500 per other dependent.
- Don’t ignore Step 2 when you or your spouse hold a second job.
- Don’t submit a new W-4 to cancel an IRS lock-in letter, because only the IRS can release it.
- Don’t wait for year-end to fix under-withholding, because the IRC §6654 underpayment penalty already accrues.
Pros and Cons of Updating a W-4 in Gusto
- Pro: The entire update is paperless, e-signed, and stored under IRS Publication 1167.
- Pro: Gusto pushes the change to the very next payroll, which is faster than most legacy HR systems.
- Pro: Gusto auto-computes withholding using current Publication 15-T tables, which reduces admin error.
- Pro: The Gusto paystub shows the new federal tax line immediately, so employees can verify the change.
- Pro: Admins get an audit log that protects the company under Treas. Reg. §31.3402(f)(2)-1.
- Con: Gusto cannot guess at your other income, so Step 4(a) still requires your own estimate.
- Con: The state certificate is a separate save, so one-stop updates are not possible in most states.
- Con: The wizard only supports the post-2020 W-4, so older allowance thinking does not transfer.
- Con: A misclicked filing status is not flagged, and Gusto will run the wrong bracket table until you fix it.
- Con: Lock-in letters are handled by admins only, so employees cannot self-correct those records.
Key Entities Behind a Gusto W-4
The Internal Revenue Service designs the form, publishes the withholding tables, and issues lock-in letters. The U.S. Treasury receives the withheld dollars and issues refunds. Gusto is the payroll platform that stores the W-4, runs payroll, and files the Form 941 with the IRS every quarter.
The employer is the legal withholding agent under IRC §3402 and is personally liable under IRC §3403 for under-withheld amounts. The employee is the certifier of the W-4 and can face a civil penalty under IRC §6682 for a false form.
State revenue agencies, such as the California Employment Development Department and the New York Department of Taxation and Finance, run parallel state forms that Gusto stores alongside the federal W-4.
Relevant Precedent and Rulings
In Slodov v. United States, 436 U.S. 238 (1978), the Supreme Court reinforced that withheld payroll taxes are held in trust for the United States and cannot be diverted by the employer. That ruling is why Gusto remits withholding on strict IRS deadlines. It also explains the personal liability that falls on responsible persons under IRC §6672.
In United States v. Malinowski, 347 F. Supp. 347 (E.D. Pa. 1972), a false W-4 claim led to criminal conviction, which remains the leading warning against fake exempt claims. Admins and employees should treat every W-4 as sworn under penalty of perjury, just as the signature block on Form W-4 states.
FAQs
How long does it take for a new W-4 to show up in my paycheck in Gusto?
Yes, a W-4 saved before the payroll cutoff, which is usually two business days before payday, will appear on the very next paycheck based on the current Publication 15-T tables.
Can my employer refuse to accept my updated W-4?
No, the employer must accept a valid signed W-4 under Treas. Reg. §31.3402(f)(2)-1, unless the IRS has issued a lock-in letter that overrides the employee’s form.
Can I claim exempt from federal withholding on my Gusto W-4?
Yes, but only if you had zero tax liability last year and expect zero this year, per the Form W-4 instructions; a false claim triggers a $500 penalty under IRC §6682.
Does updating my federal W-4 in Gusto also update my state withholding?
No, state withholding certificates like the DE-4 or IT-2104 are separate forms that you must save individually inside Gusto.
Can an admin update a W-4 without the employee’s signature?
No, Gusto requires a signed paper or electronic W-4, and Treas. Reg. §31.3402(f)(2)-1 requires a signed writing before the employer may act on it.
Do I need to update my W-4 every year?
No, you are not required to update every year, but the IRS in Publication 505 urges a fresh W-4 after any life, job, or income event.
Will my new W-4 in Gusto change my last paycheck of the prior year?
No, the W-4 only affects payrolls dated after the save, because withholding is a pay-as-you-earn system under IRC §3402.
Can I set a flat dollar federal withholding on Gusto?
Yes, by using Step 4(c) of the W-4 to add extra per-paycheck withholding, which is the most precise way to hit a target under Publication 15-T.
What happens if I ignore an IRS lock-in letter sent to my employer?
No, you cannot ignore it; the employer must follow Letter 2800C within 60 days or risk personal liability under IRC §3403.
Can I use the IRS Tax Withholding Estimator alongside Gusto?
Yes, the IRS Tax Withholding Estimator gives you an exact dollar number to enter into Step 4(c) of the Gusto W-4 wizard.
Does Gusto store a copy of my signed W-4?
Yes, Gusto stores the e-signed W-4 under IRS Publication 1167 rules, and you can download the PDF any time from your profile.
Can I undo a W-4 change I just saved in Gusto?
Yes, you can submit another W-4 at any time, and the newest valid signed form replaces the prior one under Treas. Reg. §31.3402(f)(2)-1.
Related reading
- Can a W-4 Be Updated at Any Time? (w/Examples) + FAQs
- How to Update a W-4 in ADP (w/Examples) + FAQs
- How to Update a W-4 in Paychex (w/Examples) + FAQs
- How to Update a W-4 in Paycor (w/Examples) + FAQs
- How to Update a W-4 in Paylocity (w/Examples) + FAQs
- How to Update a W-4 in Workday (w/Examples) + FAQs
- How to Fill Out a W-4 to Not Owe Taxes (w/Examples) + FAQs