A tax gross up is a payroll calculation that runs in reverse: instead of starting with a gross wage and subtracting taxes to find the net, the employer starts with the net amount the employee should receive and works backward to find the larger gross payment that, after withholding, leaves exactly that net in the employee’s pocket. Employers use it when they’ve promised a specific take-home figure, most often on a bonus, severance check, relocation reimbursement, or taxable fringe benefit.
The math is not as simple as adding the tax rate on top of the net. Say you want to hand someone $10,000 after tax and the combined rate is 30%. Add 30% and you’d pay $13,000, but taxes now apply to $13,000, not $10,000, so withholding rises to $3,900 and the employee only nets $9,100. The extra money added to cover tax is itself taxable. A gross up formula closes that loop in one step.
The Gross Up Formula
The standard formula is:
Gross Payment = Net Payment ÷ (1 − Combined Tax Rate)
The combined tax rate is the sum of every withholding percentage that applies to the payment: federal income tax on supplemental wages, the employee’s share of Social Security and Medicare, and any state or local income tax. Enter the total as a decimal and the formula returns the full gross amount.
A Worked Example
An employer wants to pay a $10,000 net bonus. The applicable rates are:
- Federal supplemental withholding: 22%
- Social Security: 6.2%
- Medicare: 1.45%
- State income tax: 5%
The combined rate is 34.65%. The formula gives $10,000 ÷ (1 − 0.3465) = $10,000 ÷ 0.6535 = $15,302.22. The employer pays $15,302.22 in gross wages. After $5,302.22 is withheld across the four tax categories, the employee nets exactly $10,000. The entire $15,302.22, not just the original $10,000, is taxable wages on the employee’s W-2.
Which Tax Rates Go Into the Combined Rate
Federal Supplemental Withholding
The IRS treats gross-up payments as supplemental wages, which lets employers withhold federal income tax at a flat 22% rather than running the payment through the employee’s W-4. That 22% rate was permanently locked in by P.L. 119-21. If total supplemental wages paid to one employee exceed $1 million during the calendar year, everything above that threshold is withheld at 37%.1Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide – Section: 7. Supplemental Wages
The 22% is a withholding convenience, not a final tax. More on that at the end.
FICA
The employee’s FICA share is 7.65%: 6.2% Social Security plus 1.45% Medicare.2Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates Both go into the combined rate, subject to the wage thresholds below.
State and Local
State supplemental rates vary widely. Some states have no income tax; others impose flat supplemental rates ranging from roughly 1.5% to nearly 12%. A handful of jurisdictions add local income tax. Each applicable rate gets added to the combined rate, which is why the same $10,000 net bonus costs the employer noticeably more in a high-tax state than in a no-tax one.
High-Earner Adjustments
Two wage thresholds can change the combined rate for large payments or highly compensated employees.
Social Security Wage Base
Social Security tax applies only to the first $184,500 of an employee’s earnings in 2026.3Social Security Administration. Contribution and Benefit Base Once year-to-date wages hit that ceiling, the 6.2% withholding stops for the rest of the year. If an employee has already passed the cap before the gross-up payment, Social Security drops out of the combined rate entirely, lowering the gross-up amount. If the payment itself pushes the employee over the limit, the calculation splits: 6.2% applies to the portion below the cap, 0% above it. Payroll systems usually handle the split automatically.
Additional Medicare Tax
An extra 0.9% Medicare surtax applies to wages above $200,000 in a calendar year. Employers use the $200,000 mark regardless of the employee’s filing status; the $250,000 married-filing-jointly threshold is a return-level figure, not a withholding one.4Internal Revenue Service. Topic No. 560, Additional Medicare Tax That raises Medicare withholding from 1.45% to 2.35% on the portion above the threshold. Employers begin withholding it in the pay period that crosses $200,000 and continue through year-end. There is no employer match on the surtax.5Internal Revenue Service. Understanding Employment Taxes
For a high-earner gross up, the combined rate may exclude Social Security (already past the cap) but include the 0.9% surtax. Getting the combined rate wrong in either direction means the employee doesn’t net the promised amount or the employer overpays.
When Employers Use a Gross Up
Bonuses and Severance
Employment agreements often guarantee a specific after-tax bonus or severance figure. Grossing up preserves the promised value regardless of where the employee lives or what bracket they land in. It also standardizes offers: a $50,000 net signing bonus means the same thing to a candidate in a no-income-tax state and one in a high-tax jurisdiction.
Relocation Packages
Employer-paid moving costs, temporary housing, and house-hunting trips are taxable income to the employee. The Tax Cuts and Jobs Act suspended the qualified moving expense exclusion, and P.L. 119-21 made the suspension permanent for all taxable years beginning after 2017.6U.S. Congress. Public Law 119-21 – Section 70113 The only exception is for members of the U.S. Armed Forces and certain intelligence community personnel. For everyone else, relocation reimbursements are fully taxable, and gross ups are a standard part of relocation offers so an employer-initiated move doesn’t leave the employee with a surprise tax bill.
Taxable Fringe Benefits
Any fringe benefit the law doesn’t specifically exclude is taxable and must be included in the employee’s pay.7Internal Revenue Service. Publication 15-B (2026), Employer’s Tax Guide to Fringe Benefits – Section: Are Fringe Benefits Taxable? Personal use of a company vehicle and employer-provided group-term life insurance coverage above $50,000 are common triggers. The employee owes tax on income they never received as cash, so employers frequently gross up the amount so the benefit doesn’t reduce take-home pay.
What the Gross Up Costs the Employer
The grossed-up payment on the employee’s paystub isn’t the employer’s full expense. The formula only accounts for the employee’s withholding; the employer’s own payroll taxes sit on top.
- Employer FICA match of 7.65% on the grossed-up wages, subject to the same $184,500 Social Security cap. No employer match on the 0.9% Additional Medicare Tax.8Internal Revenue Service. Publication 926 (2026), Household Employer’s Tax Guide
- Federal unemployment tax (FUTA), typically an effective 0.6% on the first $7,000 of annual wages after state credits. For most established employees, year-to-date wages have already passed $7,000 and FUTA adds nothing, but it matters for a large payment early in the year.9U.S. Department of Labor. FUTA Credit Reductions
- State unemployment tax (SUTA), with wage bases ranging from $7,000 to over $78,000 depending on the state. Like FUTA, only relevant if the employee hasn’t yet reached the state wage base.
For a mid-year $10,000 net bonus to someone already past the FUTA and SUTA bases but below the Social Security cap, the employer’s outlay is roughly the grossed-up payment plus about 7.65% of that payment in matching FICA.
How the Payment Shows Up in Payroll Reporting
The full grossed-up amount, not the net, is what goes on the employee’s Form W-2. It flows into Box 1 as wages, into Box 3 as Social Security wages (capped at $184,500 for 2026), and into Box 5 as Medicare wages with no cap. Taxes withheld appear in Boxes 2, 4, and 6.10Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3 The same grossed-up wages roll into the quarterly Form 941, and the IRS reconciles the two.11Internal Revenue Service. Instructions for Form 941
A Gross Up Doesn’t Always Settle the Final Tax Bill
A gross up guarantees a net amount at the time of payment. It doesn’t guarantee the employee’s year-end liability comes out even. The 22% federal supplemental rate is flat withholding, not a personalized calculation. An employee in the 32% or 35% bracket has been under-withheld on the payment and will owe the difference at filing. Someone in the 12% bracket has been over-withheld and will see a larger refund.
State taxes work the same way. Some employers use the employee’s actual marginal rate; others use the state’s flat supplemental rate, which may not match. If you receive a grossed-up payment, review your overall withholding and consider adjusting your W-4 or making an estimated payment if the rates used don’t line up with your actual bracket. The gross up handles the withholding math cleanly at the moment of payment; your annual return settles whatever’s left.