The Complete Guide to Form W-4 Step 4(c)
What extra withholding means, when to use it, and how to estimate a per-paycheck amount for common income changes.
Form W-4 Step 4(c) is where you request an additional dollar amount to be withheld from each paycheck. It can help address multiple jobs, bonuses, RSUs, side income, or a prior-year withholding gap. The amount should come from a current estimate—not a guess—and should be divided across the paychecks remaining in the tax year.
Step 4(c) versus Steps 4(a) and 4(b)
Step 4(a) adds other income, Step 4(b) accounts for deductions, and Step 4(c) adds a dollar amount per pay period. They solve different problems and should not be used interchangeably.
Three calculation scenarios
Round the final amount to a practical payroll-friendly value and recheck after the next paystub.
- • Dual income: estimate the household gap and divide it across one or both jobs.
- • RSUs or bonuses: compare supplemental withholding with projected annual liability.
- • 1099 income: include income tax and self-employment tax after expenses.
Common mistakes
Using last year’s amount without checking income changes, entering an annual amount instead of a per-paycheck amount, forgetting pay frequency, and ignoring state withholding are common errors.
How to verify it
After one or two pay cycles, compare the new withholding with the expected amount. At the next quarterly checkpoint, update the estimate if income or payroll assumptions changed.
Use the planning tool
Run your own withholding check with current income, paystub, filing status, and paychecks remaining.
Open Withholdwise