W-4 Step 4(c) Extra Withholding: When, How Much, and Paycheck Impact

Step 4(c) on Form W-4 is the line where you tell your employer to withhold an extra flat dollar amount for federal income tax from every paycheck. Whatever number you write there is added on top of the withholding your employer already calculates from your filing status and the rest of the form, and it keeps coming out of each check until you submit a new W-4. That single line is the simplest way to use W-4 extra withholding to cover income no employer is withholding against, close the gap when you hold more than one job, or steer clear of an underpayment penalty at filing time.

When to Add Extra Withholding

The standard withholding formula assumes the job you’re filling out the W-4 for is your only source of income. When that assumption breaks, you owe more at filing than your paychecks covered. A few common situations trigger it:

Interest, dividends, capital gains, rental income, and retirement account distributions all create tax that no employer withholds against. Rather than making quarterly estimated payments, you can cover that tax through your paycheck.
Freelance or gig income carries both income tax and self-employment tax. If you also hold a W-2 job, bumping Step 4(c) can replace or supplement quarterly payments.
With two or three jobs, each employer withholds as if its wages were your only income, so combined withholding almost always falls short.
Increasing withholding is one of the most reliable ways to stay above the IRS safe harbor and avoid the underpayment penalty.

The IRS explicitly points to Step 4(c) as the line for employees who want more tax withheld, and notes that people with income not subject to withholding can choose to have more taken from their paycheck instead of making estimated payments.¹²

How to Figure Out the Right Dollar Amount

Using the IRS Tax Withholding Estimator

The fastest way is the IRS Tax Withholding Estimator at irs.gov. You enter your wages, other income, deductions, and credits, and the tool projects your annual tax against what’s already been withheld. It then generates a pre-filled W-4 with a recommended Step 4(c) amount designed to bring you close to even at filing.³ Have your most recent pay stubs, your spouse’s stubs if applicable, and last year’s Form 1040 in front of you. If your pay changes significantly during the year, run it again and submit a new W-4.⁴

The Estimator usually populates only one or two lines rather than every line in Step 4. It may fill Step 3 to reduce withholding, Step 4(c) to increase it, or Step 4(a) or 4(b) to adjust the taxable amount. You generally don’t need more than two entries.¹

Doing the Math Yourself

Three steps. First, estimate your total federal income tax for the year from every source: wages, freelance income, investment income, retirement distributions, everything. Last year’s return adjusted for known changes is a fine starting point. Second, estimate how much federal tax will be withheld from your wages under your current W-4. Multiply your per-paycheck withholding by the total pay periods in the year. Third, subtract expected withholding from expected total tax. A positive result is your shortfall.

Divide that shortfall by the pay periods you have left in the year. That’s your Step 4(c) amount. If you expect $3,600 in tax on freelance income and have 24 biweekly checks left, enter $150. At the start of the next year, recalculate against the full 26 pay periods so the per-check amount reflects a full year instead of a partial one.

One threshold to watch. If your adjusted gross income on last year’s return exceeded $150,000 ($75,000 if married filing separately), the safe harbor based on last year’s tax rises from 100% to 110%. Run your numbers against that higher figure, not the standard one.⁵

How Step 4(c) Fits With the Rest of the W-4

The W-4 gives you several ways to handle multiple jobs and outside income, and they can overlap. A quick tour so you don’t double up:

The Step 2(c) checkbox tells payroll to cut your standard deduction and tax brackets in half, assuming two roughly equal jobs. If the jobs pay similar amounts, that alone works. If one pays much more, the checkbox over-withholds, and Step 4(c) gives you finer control.⁶
The Step 2(b) Multiple Jobs Worksheet produces a number that goes directly onto Step 4(c) for your highest-paying job. You can add more on top of the worksheet result if you want.
Step 4(a) increases the income figure that runs through the withholding formula. It’s similar in effect to Step 4(c), but works through the tax calculation instead of as a flat add-on. If you’d rather not disclose other income on Step 4(a), the IRS says you can skip it and put an equivalent amount on Step 4(c) instead.⁶
Step 3 reduces withholding for tax credits. It and Step 4(c) work in opposite directions and net against each other, which is why the Estimator populates one or the other, not both.¹

If you hold more than one job or receive a pension, put all Step 3, 4(a), 4(b), and 4(c) amounts on the W-4 for the highest-paying position. Leave those lines blank on the other W-4s so the other jobs withhold at standard rates based on filing status.¹

Why Withholding Beats Estimated Payments for Penalty Purposes

You avoid the underpayment penalty if your withholding and estimated payments during the year cover at least the lesser of 90% of your current-year tax or 100% of last year’s (110% at the higher-income threshold above).⁷⁵

Here’s where Step 4(c) has a real edge over quarterly estimated payments. Federal tax withheld from wages is treated as paid evenly across the year, regardless of when the withholding actually happened.⁵ Estimated payments are credited to the quarter you paid them. If you realize in October that you’re behind, increasing Step 4(c) for the last two months effectively spreads that tax back across the whole year for penalty purposes. A single October estimated payment can’t do that.

What It Looks Like on Your Paycheck

Your Step 4(c) amount is a flat dollar figure added to every paycheck. Payroll first calculates standard withholding from filing status, Step 2, Step 3 credits, and the taxable wages from Steps 4(a) and 4(b). Then it adds your Step 4(c) amount.⁸ If you entered $150, exactly $150 extra comes out every pay period, whether you worked overtime or took unpaid leave.

It isn’t a percentage. That predictability is helpful for budgeting, but it also means the number doesn’t shrink automatically if your hours drop. A $200 extra withholding that fit a full-time paycheck can eat a painful share of a reduced check during a slow period.

Bonuses and Other Supplemental Wages

Bonuses, commissions, and other supplemental wages can be taxed differently. Employers may withhold on supplemental wages at a flat 22% (37% on amounts over $1 million in a calendar year) rather than running the payment through the standard W-4 calculation.⁹ When an employer uses that flat rate method, the Step 4(c) amount may not be added to the bonus withholding. The alternative method, which combines the bonus with regular wages and calculates withholding on the total, does apply your full W-4 settings including Step 4(c). Which method your employer uses depends on their payroll setup, so if you receive large bonuses, ask payroll whether your extra withholding hits those payments or only regular checks.

State Withholding Is Separate

The federal W-4 changes federal withholding only. It does not touch your state income tax withholding. Most states with an income tax use their own withholding form, and many have their own extra-withholding line. If you need to cover state tax on outside income, file the state form with your employer in addition to the federal W-4.

Changing or Stopping Extra Withholding

To change your Step 4(c) amount, submit a new W-4 to your employer. Payroll can’t adjust withholding without a signed, updated form.⁸ To stop it entirely, enter $0 on line 4(c) or leave it blank. Once you turn in the form, your employer must implement the change no later than the first payroll period ending on or after 30 days from the date they received it.¹⁰ Most payroll departments do it within one or two pay cycles.

Revisit the amount whenever your picture shifts: marriage or divorce, starting or ending side work, losing a second job, a big investment gain, or a significant pay change at the primary job. The earlier you update, the more evenly the adjustment spreads across your remaining paychecks. Waiting until November to fix a shortfall means cramming the full correction into a handful of checks.

When the IRS Locks In Your Withholding

In rare cases, the IRS decides an employee’s withholding is too low and sends a lock-in letter (Letter 2800-C) to the employer. While a lock-in is in effect, your employer must withhold at the rate the IRS specifies and cannot honor a new W-4 that would drop withholding below that rate.¹¹ You can still submit a W-4 requesting more than the lock-in amount, including through Step 4(c), and your employer must honor the increase. Any request to go below the lock-in rate requires IRS approval first. If you receive a companion notice (Letter 2801-C), contact the IRS directly to resolve it rather than trying to override it through payroll.

1
Internal Revenue Service. Tax Withholding Estimator FAQs
2
Internal Revenue Service. Pay As You Go, So You Won’t Owe
3
Internal Revenue Service. Tax Withholding Estimator
4
Internal Revenue Service. FAQs on the 2020 Form W-4
5
Office of the Law Revision Counsel. 26 USC 6654
6
Internal Revenue Service. Form W-4, Employee’s Withholding Certificate
7
Internal Revenue Service. Topic No. 306, Penalty for Underpayment of Estimated Tax
8
Internal Revenue Service. About Form W-4
9
Internal Revenue Service. Publication 15 (2026), Employer’s Tax Guide
10
Internal Revenue Service. Topic No. 753, Form W-4
11
Internal Revenue Service. Withholding Compliance Questions and Answers