How to fill out your W-4 when you have side gig income

Updated for the 2026 tax year

If you have a regular W-2 job and also drive for Uber, deliver for DoorDash, or freelance on the side, you have a choice most full-time 1099 workers don't: you can use your W-2 job's withholding to cover the tax on your side income, instead of making quarterly estimated payments yourself. This guide walks through exactly how, using Line 4(c) of Form W-4.

Why this works

The IRS treats withholding differently from estimated payments in one important way: withholding is considered to have been paid evenly across all four quarters of the year, no matter when during the year it was actually withheld. Estimated payments, by contrast, only count for the quarter you actually send them in.

This means if you under-withhold early in the year and then increase your withholding in October, that increased withholding retroactively "fixes" your earlier quarters in the eyes of the IRS — something a late estimated payment can't do once a quarterly deadline has already passed. It's a meaningful advantage if you only have side income that's hard to predict early in the year.

Step 1: figure out how much extra tax your side income creates

Your 1099 income doesn't just owe regular income tax — it also owes self-employment tax (15.3%, covering both halves of Social Security and Medicare that an employer would normally split with you). Between the two, gig income is taxed more heavily than the same amount of W-2 wages.

That last number — the extra tax your gig income creates, including both the additional federal income tax and the full self-employment tax — is what you need your W-2 withholding to cover.

Step 2: spread it across your remaining paychecks

Once you know the total extra tax your side income creates for the year, divide it by the number of paychecks you have left in the year. That per-paycheck number is what goes on Line 4(c).

Step 3: actually fill out the form

1. Get a blank Form W-4 from your employer or IRS.gov. You don't need to redo your entire W-4 — you're typically just adding or updating one line.
2. Complete Steps 1(a) and 1(b) with your name, address, and filing status as usual.
3. Skip Steps 2 and 3 unless they already apply to your situation (Step 2 is for multiple jobs or a working spouse; Step 3 is for dependents).
4. On Line 4(c), enter your calculated per-paycheck amount — this is "extra withholding" and it's added on top of whatever your employer would normally withhold based on your wages.
5. Sign and date it, then give it to your employer's payroll or HR department. They'll apply it starting with your next paycheck, or sometimes the one after that depending on their processing schedule.

When this approach doesn't fully work

This strategy assumes you have a steady W-2 paycheck to withhold from for the rest of the year. A few situations complicate it:

• You don't have a W-2 job at all, or it's seasonal. If your only income is 1099, there's no paycheck to add Step 4(c) withholding to, and you'll need to make quarterly estimated payments directly to the IRS instead.
• Your gig income varies wildly month to month. The calculation above assumes your side income for the rest of the year looks roughly like what you've already estimated. A big swing — a slow month or an unexpectedly large freelance contract — will throw off the math and may require a mid-year adjustment.
• You're already close to the end of the year. The fewer paychecks you have left, the larger the per-paycheck adjustment needs to be to catch up. If you're adjusting in November for income earned since January, expect a noticeably bigger number than if you'd adjusted in March.

What about state tax?

This entire approach covers federal withholding only. If you live in a state with its own income tax — California and New York both tax gig income, for example — you'll generally need a separate state withholding adjustment or your own state estimated payments to stay current there. Federal Form W-4 doesn't touch your state tax situation.

The bottom line

If you have both a W-2 job and gig income, adjusting your W-4 instead of juggling quarterly estimated payments is often the simpler path — one form, one number, and your employer handles the rest for the remainder of the year. It's not the right fit for everyone, particularly if your only income is 1099 or your gig earnings swing unpredictably, but for a steady side hustle alongside a regular job, it can replace quarterly payments entirely.

This article is for general informational purposes only and does not constitute tax, legal, or financial advice. The calculations described do not model state income tax, the Additional Medicare Tax, itemized deductions, or additional tax credits. Tax rules are complex and change frequently. Consult a qualified tax professional before submitting a new Form W-4.