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 (since Step 4a only covers income tax, not SE tax), 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 →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.