How to Calculate a Gross-Up Bonus: Formula, FICA, and Reporting

To calculate a gross-up bonus, divide the target net amount by one minus the employee’s combined tax rate. If you want an employee to take home $10,000 and their combined federal, FICA, and state withholding rate is 34.65%, the gross payment is $10,000 ÷ (1 − 0.3465) = $15,302.22. Payroll withholds $5,302.22 in taxes, and the employee deposits exactly $10,000. The formula looks simple because it already absorbs the tricky part: the taxes the employer pays on the employee’s behalf are themselves taxable wages, and the single division handles that tax-on-tax loop in one step.¹

The Formula

Gross Amount = Net Amount ÷ (1 − Combined Tax Rate)

Everything hinges on the combined tax rate. That number is the sum of every withholding rate that applies to the bonus: federal income tax, Social Security, Medicare, and any state or local income tax. Get the rate right and the formula does the rest.

Building the Combined Tax Rate for 2026

Four components go into the combined rate.

Federal income tax. Bonuses are supplemental wages, and most employers withhold at the flat 22% supplemental rate. That rate holds until an employee’s total supplemental wages for the calendar year exceed $1 million; above that threshold, the excess must be withheld at 37%.² The alternative is the aggregate method, which combines the bonus with the employee’s most recent regular paycheck and applies the standard tax tables using the W-4 on file. Aggregate is more work but tracks the employee’s actual marginal rate, so the gross-up doesn’t leave the employee underwithheld at year end if their bracket is well above 22%.

Social Security. 6.2% of wages up to the 2026 wage base of $184,500. Once the employee’s year-to-date earnings clear that ceiling, Social Security drops to zero on any additional wages for the rest of the year.³

Medicare. 1.45% on all wages with no cap. An additional 0.9% must be withheld on wages above $200,000 in a calendar year, regardless of the employee’s filing status.⁴

State and local. Rates vary widely. Some states set a flat supplemental rate anywhere from roughly 1.5% to over 11%; others make you use their progressive tables. Nine states have no income tax. Local taxes stack on top in the jurisdictions that impose them, and every applicable local rate belongs in the combined rate before you run the formula.

Add the components: 22% + 6.2% + 1.45% + 5% state = 34.65%. That is the number you plug into the denominator.

A Worked Example

An employee has earned $90,000 year-to-date, well below the Social Security wage base and the Additional Medicare threshold. The employer wants to guarantee $10,000 net and operates in a state with a 5% flat supplemental rate.

Combined rate: 22% + 6.2% + 1.45% + 5% = 34.65%
Gross amount: $10,000 ÷ 0.6535 = $15,302.22
Federal withholding at 22%: $3,366.49
Social Security at 6.2%: $948.74
Medicare at 1.45%: $221.88
State at 5%: $765.11
Total withheld: $5,302.22
Net to employee: $10,000.00

Every dollar of that $5,302.22 is reported as additional wages on the employee’s W-2. The formula worked because a single combined rate applied cleanly to the entire bonus.¹

When the Single-Rate Formula Breaks Down

The clean algebraic version assumes one combined rate applies to every dollar of the bonus. That assumption fails whenever the bonus crosses a threshold mid-payment.

Social Security wage base. An employee at $180,000 year-to-date receiving a gross-up bonus hits the 6.2% Social Security ceiling after the first $4,500 of new wages. Wages beyond $184,500 are not subject to Social Security.⁵

Additional Medicare Tax. An employee at $195,000 year-to-date pays 1.45% Medicare on the first $5,000 of the bonus, then 2.35% on everything above $200,000.⁶

Supplemental wages over $1 million. The federal rate jumps from 22% to 37% on the excess, changing the combined rate sharply at that line.²

In each case, no single rate produces the correct gross amount. The fix is iterative. Start with an estimate from the formula, calculate the actual taxes owed on that estimate by applying the correct rate to each portion above and below the threshold, check whether the resulting net matches the target, and adjust. Repeat until the net lands on the target. Payroll software handles this automatically, but the logic is worth understanding when you need to verify a result or explain it to the employee.

FICA Applies to the Full Grossed-Up Amount

Both Social Security and Medicare apply to the entire gross figure, not just the net bonus. So does federal income tax withholding. That is why the combined rate in the denominator has to include all of them; leave one out and the employee’s net falls short.

The $200,000 Additional Medicare withholding threshold is the employer’s obligation and does not track filing status. The employee’s actual liability threshold at tax time may differ ($250,000 for married filing jointly, $125,000 for married filing separately), but the employer withholds at $200,000 for every employee.⁶

The Employer’s Own Cost on Top

The grossed-up wage is not the full price. The employer also owes its own matching share of FICA: 6.2% Social Security up to the wage base, and 1.45% Medicare on all wages.⁷ The 0.9% Additional Medicare Tax is employee-only; the employer does not match it.

Federal unemployment tax (FUTA) is 6.0% on the first $7,000 of wages per employee, reduced to an effective 0.6% after the standard state credit.² Most employees receiving gross-up bonuses have already cleared the $7,000 FUTA base earlier in the year, so FUTA often does not apply to the bonus itself. State unemployment wage bases run from $7,000 to $68,500 depending on the state; same logic, different threshold.

Back to the example. To deliver $10,000 net, the employer pays $15,302.22 in gross wages, plus its own $948.74 Social Security match and $221.88 Medicare match. All-in cost: about $16,472.84. A workable rule of thumb for budgeting: a gross-up costs the employer roughly 60% to 80% more than the target net, depending on the rates involved.

Watch Out for 401(k) Deferrals

If the employee has an automatic 401(k) deferral percentage and bonuses count as deferral-eligible compensation, that percentage will come out of the grossed-up payment. A 6% automatic deferral on a $15,302 gross bonus routes $918 to the 401(k) and drops the take-home below the promised net.

Two fixes. Some payroll systems let you code bonus payments as non-deferral-eligible, if the plan document allows. Otherwise, treat the 401(k) percentage as another “deduction” in the combined rate so the formula grosses up enough to cover both taxes and the retirement contribution. Which approach is right depends on the plan document and on whether the employee actually wants the deferral applied to the bonus. This is one of the most common reasons a grossed-up payment misses its target.

Reporting the Bonus

W-2

The full grossed-up amount is the employee’s taxable wage, not just the net. Report the gross in Box 1 (Wages, Tips, Other Compensation), Box 3 (Social Security Wages, capped at $184,500 for 2026), and Box 5 (Medicare Wages and Tips). The taxes actually withheld go in Box 2, Box 4, and Box 6.⁸ Because the employer covered the withholding on the employee’s behalf, the W-2 reflects both the full gross and the full withholding, leaving nothing for the employee to reconcile at filing.

Form 941

Grossed-up wages flow through the quarterly Form 941 the same way any other wages do: Line 2 for total wages, Line 3 for federal income tax withheld, Line 5a for Social Security wages, and Line 5c for Medicare wages.⁹ The 941 amounts should reconcile with the W-2 at year end, and the deposit rules in Publication 15 govern when the withheld taxes are due.

A Note on Non-Cash Gross-Ups

The same math applies to relocation reimbursements and taxable fringe benefits (personal use of a company car, high-value gifts, and similar items). Determine the fair market value of the benefit, treat that value as the “net” starting point, and run the formula. Reporting mechanics are identical to a cash bonus.¹⁰

1
Internal Revenue Service. Publication 525 (2025), Taxable and Nontaxable Income
2
Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide
3
Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates
4
Internal Revenue Service. Questions and Answers for the Additional Medicare Tax
5
Social Security Administration. Contribution and Benefit Base
6
Internal Revenue Service. Topic No. 560, Additional Medicare Tax
7
Social Security Administration. Social Security and Medicare Tax Rates
8
Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3
9
Internal Revenue Service. Instructions for Form 941
10
Internal Revenue Service. IRS Relocation Travel Guide