To gross up a paycheck, add together every tax rate that will be withheld from the payment, subtract that total from 100% to get the net percentage the employee actually keeps, and divide the target take-home amount by that decimal. The result is the gross figure you enter into payroll so the employee’s net check lands exactly where you promised.
Everything else is getting the rates right and handling the edges. The math itself is one line.
The Formula
Gross pay = Target net ÷ (1 − total tax rate)
The “total tax rate” is the sum of every percentage that will be deducted from the employee’s wages on this payment. Employer-side taxes never enter the formula because they don’t come out of the employee’s check. That excludes FUTA, which is employer-only at an effective 0.6% on the first $7,000 of annual wages,1Internal Revenue Service. Topic No. 759, Form 940 – Employers Annual Federal Unemployment (FUTA) Tax Return along with the employer share of Social Security and Medicare.
Tax Rates to Gather Before You Calculate
Leaving out a single component means the employee’s check comes in short. Pull each of these before you touch the formula.
Federal Income Tax on Supplemental Wages
The IRS sets a flat 22% withholding rate on supplemental wages such as bonuses, commissions, and awards, provided the employee has received no more than $1 million in total supplemental wages for the calendar year. Anything above $1 million is withheld at 37%, regardless of the employee’s W-4.2Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide
The 22% flat rate is only available if you actually withheld income tax from the employee’s regular wages in the current or immediately preceding calendar year. If you didn’t, you have to use the aggregate method, which combines the supplemental payment with the employee’s regular wages and calculates withholding on the total as though it were one paycheck.2Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide Aggregate-method gross-ups don’t have a clean flat rate to plug into the formula, so most employers reach for payroll software or an iterative calculation instead.
Social Security
The employee share of Social Security tax is 6.2% of wages up to the annual wage base.3Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax For 2026 the base is $184,500.4Social Security Administration. Contribution and Benefit Base Check the employee’s year-to-date earnings first. If they’ve already crossed the base, Social Security drops out of the formula entirely. If they’re close, only the part of the grossed-up payment that fits under the cap gets the 6.2%, and you’re into a split calculation.
Medicare
Medicare is 1.45% on all wages, no cap.5Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates Once the employee’s year-to-date wages cross $200,000, employers must withhold an additional 0.9% on wages above that threshold, bringing the effective Medicare rate on that portion to 2.35%.6Internal Revenue Service. Topic No. 560, Additional Medicare Tax If your gross-up straddles the $200,000 line, the payment has to be split at the threshold.
State and Local
Most income-tax states publish a supplemental withholding rate for bonuses, running roughly from 1.5% to over 11%. Some states require the employee’s regular rate instead, mirroring the federal aggregate method. Certain cities and counties impose their own income taxes on top. Use the rates for the employee’s work location, not their home address unless local rules say otherwise.
A Worked Example
Target net bonus: $1,000. Applicable rates: 22% federal supplemental, 6.2% Social Security, 1.45% Medicare, 5.35% state.
Step 1. Add the rates: 22 + 6.2 + 1.45 + 5.35 = 35%.
Step 2. Subtract from 100% to get the net percentage: 100% − 35% = 65%, or 0.65 as a decimal. That’s the share of each gross dollar the employee keeps.
Step 3. Divide the target net by the net percentage: $1,000 ÷ 0.65 = $1,538.46. Enter $1,538.46 as the gross.
When payroll withholds 35% of $1,538.46, it takes $538.46 in taxes and pays out exactly $1,000. Scale it up the same way: a $5,000 target at 35% combined comes to $5,000 ÷ 0.65 = $7,692.31 gross.
Why You Can’t Just Add the Tax Percentage to the Net
Tacking 35% onto $1,000 to get $1,350 seems like the same thing. It isn’t. Withholding 35% of $1,350 pulls $472.50 in taxes and leaves the employee with $877.50, not $1,000. Taxes come off the gross, and the gross has to include the tax on itself. The division method handles that loop; simple addition doesn’t.
When One Flat Rate Won’t Work
The single-divisor formula only works when every applicable rate hits the entire payment. Two situations break that assumption:
- Wage-base caps. If the employee has earned $180,000 year-to-date, only the first $4,500 of the grossed-up bonus is subject to Social Security. The rest faces only income tax and Medicare, so the effective rate changes partway through the payment.
- The $200,000 Additional Medicare threshold. Wages below the line are hit at 1.45%; wages above are hit at 2.35%. If the bonus crosses the line, no single blended rate is accurate.
Both situations call for an iterative approach: estimate a gross, compute the actual taxes, compare the net to the target, adjust, repeat until it converges. Payroll software does this automatically. If you’re doing it by hand, the IRS references formulas for employer-paid-tax scenarios in Publication 15-A and Revenue Procedure 83-43. For the standard bonus to an employee well under both thresholds, the plain division formula is fine.
Running the Payment Through Payroll
Enter the calculated gross into your payroll system as that period’s payment. The system withholds each tax, and the employee’s net should land on the target. Verify the output before finalizing; a single wrong digit in the gross field takes a full pay cycle to unwind.
The paystub will show the full gross with each tax deduction itemized. That transparency is part of the point. The employee should see that the company paid the taxes on top of the reward.
W-2 Reporting
The full grossed-up amount goes in Box 1 of the W-2, not the net the employee actually received. The IRS treats the taxes you paid on the employee’s behalf as additional compensation to that employee,7Internal Revenue Service. Publication 525 (2025), Taxable and Nontaxable Income and the W-2 instructions require reporting grossed-up withholding as supplemental wages in Boxes 1, 3, 5, and 7 as applicable.8Internal Revenue Service. 2025 General Instructions for Forms W-2 and W-3 The result is a small tax-on-tax effect at year end: the employee’s reported income exceeds the cash they took home, because the taxes the employer covered are themselves taxable to the employee.
Recordkeeping
Federal regulations require employers to keep payroll records, including the nature of every addition to or deduction from wages, for at least three years from the last date of entry.9eCFR. 29 CFR Part 516 – Records to Be Kept by Employers For each gross-up, hold on to the target net, the rates you used, the calculation itself, and the resulting gross. An auditor will want to see how the number was built, not just what the payroll register printed.
What Happens If You Get It Wrong
A miskeyed gross figure is usually fixable in the next pay period. Willfully failing to collect and pay over employment taxes is a separate problem: under federal law it is a felony carrying fines up to $10,000 and up to five years in prison.10Office of the Law Revision Counsel. 26 USC 7202 – Willful Failure to Collect or Pay Over Tax The statute targets intentional evasion, not arithmetic mistakes. Even so, gross-ups that consistently under-withhold can pull civil penalties and IRS attention without any criminal element. Building the calculation correctly the first time is cheaper than fixing it later.