Definition
Step 4c is the 'extra withholding' line on the W-4. You enter a flat dollar amount per paycheck, and your employer adds it to every withholding calculation regardless of other settings. It's the most flexible tool on the W-4 — no formulas, no income limits, no explanations required.
Common uses: covering an anticipated balance from under-withholding, building a safety buffer against April surprises, covering tax on self-employment income (the W-4 says not to put self-employment income in Step 4a, and 4a would miss the SE tax anyway), fine-tuning after using the IRS estimator, or targeting a specific refund amount.
The refund target tool in this calculator automatically calculates the Step 4c amount needed to reach any desired refund.
How this affects your W-4
Step 4c is the most direct adjustment on the W-4. Unlike Step 4a (which estimates tax on other income and adjusts withholding tables) or Step 4b (which reduces withholding for extra deductions), Step 4c adds or removes a known dollar amount per paycheck with complete predictability.
The calculator uses Step 4c for both the refund target tool and the mid-year checkup's 'fix it' recommendation.
See how step 4c — extra withholding affects your withholding
Use the free W-4 calculator to calculate your exact withholding with your specific situation.
Open the W-4 Calculator →Read the guide
W-4 Step 4(c): How Much Extra Withholding to Enter (2026)
The formula for the Step 4(c) amount, with worked examples for owing in April, bigger refunds and side income.
W-4 Step 4 Explained: Other Income, Deductions, and Extra Withholding (2026)
Step 4 is how you fine-tune for side income, itemized deductions, and extra withholding. Most people skip it — here's when you shouldn't.
W-4 for Freelancers, 1099 and Side Gig Income (2026 Guide)
Side income has no withholding, so it shows up as a surprise tax bill. Cover income tax and self-employment tax through Step 4c or quarterly estimates, with worked examples and 2026 due dates.
Related terms
W-4 Form
The IRS form employees submit to their employer to control how much federal tax is withheld.
Underpayment Penalty
An IRS penalty charged when you owe more than $1,000 and your withholding falls below safe harbor thresholds.
Tax Refund
Money the IRS returns to you when your withholding exceeds your actual tax liability for the year.