W-4 Withholding Calculator for Side Income

Have a W-2 job and 1099 income on the side? Your employer can withhold the extra federal tax for you through Form W-4, Step 4(c). This works out how much per paycheck for the paychecks left this year, and what your state adds, which needs your state's own form.

Your 2026 figures

Filing status

Married filing separately is not supported here; use the IRS estimator.

Your W-2 salary for the year

Side (1099) profit for the full year

Income from the side work less its business expenses.

State

Pay frequency

Paychecks left in 2026

Worked out from today's date; check it against your pay schedule.

Federal estimated tax already paid this year

Form 1040-ES payments for this tax year.

State estimated tax already paid this year

Optional: last year's tax, for the prior-year safe harbor

Total tax on your 2025 return

Your 2025 adjusted gross income

Over $150,000, the prior-year safe harbor is 110% instead of 100%.

Federal: Form W-4, Step 4(c)

Extra federal tax to have withheld from each remaining paycheck.

Enough to cover the tax

$150.88

per paycheck: enter $151

Enough to avoid the penalty

$112.46

per paycheck: enter $113

This leaves less than $1,000 to pay when you file, so no underpayment penalty applies (IRS Publication 505). The rest is due when you file.

Extra income tax from the side profit: $1,803
Self-employment tax on it: $2,119
Federal estimated tax already paid: −$0
Left to withhold this year: $3,923
Paychecks left: 26

State: not part of your W-4

Choose your state to see the extra state tax on your side profit.

City taxes, such as New York City's, are not included.

What this assumes

Your W-4 (and your spouse's) already withholds the right amount for the job itself, and nothing extra has been withheld yet this year.
The side profit is a full-year estimate. Withholding counts as paid evenly through the year, so catching up by December still covers the earlier quarters.
No credits, no itemized deductions, no other income. It uses 2026 federal brackets and the state table described on the methodology page.

For self-employment income, the 2026 Form W-4 recommends the IRS Tax Withholding Estimator, which also handles credits, other income and tax already withheld.

2026 Form W-4 (IRS) IRS Tax Withholding Estimator Prefer quarterly payments?

Estimates for planning, not tax, legal or financial advice. Taxorly is not affiliated with the IRS or any state tax agency. Check your figures with a licensed tax professional before you file. How we calculate · Full disclaimer