Gross up calculator: net to gross payroll, bonus gross up and the gross up formula

Grossing up is a circular problem, and that is the whole difficulty. You add money to cover the tax, but the money you added is wages, so it gets taxed too, so you have to add more, which also gets taxed. The division solves that loop in one step. The multiplication that most people reach for first solves only the first round of it.

Say you promised somebody a $5,000 net spot bonus and the applicable rates are the 22% federal supplemental rate, 6.2% social security and 1.45% Medicare. That is 29.65% combined, which leaves 70.35% of any gross reaching the employee. So the gross is $5,000 divided by 0.7035, or $7,107.32. Withhold 29.65% of that and you take $2,107.32, leaving exactly $5,000.

The tempting alternative is to take 29.65% of $5,000, get $1,482.50, and pay $6,482.50. That number is wrong by $624.82, and the employee finds out in the worst possible way: withholding on $6,482.50 comes to $1,922.06, so they receive $4,560.44 and are $439.56 short of what you promised. The error is small enough to survive a sanity check and large enough for the employee to notice.

None of this is about whether a bonus is taxed at a higher rate than salary. It is not. The 22% is a withholding rate, not a tax rate, and it squares up on the employee tax return. A gross up is an employer promise about the number that appears in a bank account on payday, which is a cash flow question rather than a tax question.

Gross ups almost always attach to supplemental wages, so the withholding rules for supplemental wages are the rules for gross ups. IRS Publication 15 defines them as wage payments that are not regular wages, and the list is longer than most people expect: bonuses, commissions, overtime pay, payments for accumulated sick leave, severance pay, awards, prizes, back pay, reported tips, retroactive pay increases, and payments for nondeductible moving expenses. Taxable fringe benefits and expense allowances paid under a nonaccountable plan are in as well.

Two entries there deserve a second look. Overtime pay is supplemental wages by default, although Publication 15 explicitly lets you treat overtime and tips as regular wages instead. And retroactive pay increases are supplemental, which catches employers who backdate a raise and run the catch up through payroll as if it were ordinary salary. If you want the mechanics of the overtime side of that, the overtime calculator works the regular rate first, which is the figure the retro payment has to be built on.

On rates, Publication 15 is unusually blunt. If you withheld income tax from that employee regular wages in the current or immediately preceding calendar year, you may "withhold a flat 22% (no other percentage allowed)". That parenthesis is the rule most gross up spreadsheets break. You cannot withhold 25% because it feels safer, and you cannot withhold 15% because the employee asked.

Above a million dollars the election disappears. Supplemental wages paid to one employee that exceed $1 million in a calendar year are withheld on at 37% "without regard to the employee's Form W-4". The detail worth writing down is how the threshold is counted: in determining supplemental wages paid during the year, you include payments from all businesses under common control. Two affiliated entities can each pay $600,000 and neither payroll will see a problem, while the employee has crossed the line by $200,000.

Gross = net / (1 - rate) is exact under one condition that nobody states out loud: the rate has to be the same on every dollar of the payment. For a $5,000 bonus paid to somebody earning $60,000, it is. For the payments where gross ups actually get used, relocation packages and executive bonuses and severance, it frequently is not.

Three thresholds break the assumption. Social security stops at $184,500 of wages for 2026, so a payment that straddles that line carries 6.2% on part of itself and nothing on the rest. The Additional Medicare Tax starts at $200,000, so a payment that crosses it picks up 0.9% partway through. And the supplemental rate itself steps from 22% to 37% at $1,000,000. In each case the marginal rate on the last dollar of the payment differs from the rate on the first dollar, and a single division cannot represent that.

The way out is to stop treating it as a formula and treat it as a fixed point: find the gross where gross minus tax(gross) equals the target net. Start with the net, compute the tax on it, add that back, recompute, and repeat. It converges in a handful of rounds because the tax rate is below 100%, and it is correct no matter how many thresholds the payment crosses. That is what the calculator at the top of this page does, and it is the reason it can disagree with the textbook formula.

Here is how much that is worth. Take an employee already paid $180,000 this year, owed a $10,000 net relocation payment, in a state with no income tax. The textbook rate is 29.65%, which says pay $14,214.64. But only $4,500 of wage base room remains, so social security takes $279.00 rather than 6.2% of the whole payment. Solve the fixed point and the answer is $13,427.82. The formula overstates the gross by $786.82, and every dollar of that is company money handed over for no reason.

Most gross up divisors are built by adding 22% and 7.65% and calling it 29.65%. Those two numbers are not the same kind of number, and treating them as one is the reason so many gross ups drift out of true.

The 22% is an election. You choose it, it is available only under the prior withholding condition, it is capped at $1 million, and it is a withholding convention that gets reconciled on the employee tax return. The 6.2% and 1.45% are statutory. Nobody elects them, they are not reconciled later in the same way, and the 6.2% switches off at a fixed wage figure that has nothing to do with this payment.

Publication 15 makes the split explicit in its treatment of taxable fringe benefits. You may withhold federal income tax on the value of a fringe benefit at the optional flat 22% supplemental rate. But for the payroll taxes the instruction is different: you "add the value of fringe benefits to regular wages for a payroll period and figure social security and Medicare taxes on the total." Same benefit, two different mechanics, because one tax lets you elect a rate and the other does not.

For anyone running the numbers on non cash benefits rather than cash payments, the imputed income calculator handles the valuation side, and it carries one wrinkle that interacts with this page: group term life imputed income is subject to FICA but federal income tax withholding on it is optional. Grossing that up means covering a FICA bill without a matching income tax bill, so the divisor is 7.65% rather than 29.65%.

Relocation is the single most common reason a small employer needs a gross up, and the law under it changed in a way most published guidance has not caught up with.

Before 2018, an employer could reimburse qualified moving expenses tax free under section 132(a)(6) of the Internal Revenue Code. The Tax Cuts and Jobs Act suspended that exclusion for tax years 2018 through 2025, with a written expiry. Every relocation policy and calculator written in that window says the same thing: employer paid moving expenses are taxable through 2025. Plenty of them still say it.

That expiry is gone. Public Law 119-21, the One Big Beautiful Bill Act, amended section 132(g)(2) at section 70113(c): it substituted "beginning after 2017" for "2018 through 2025" in the heading and struck out the words ", and before January 1, 2026" from the text. What remains is a suspension with a start date and no end date. Section 70113(d) of the same act added a second carve out alongside the existing one for active duty military moving under orders, for an employee or new appointee of the intelligence community moving under a change of assignment.

For a civilian employer the practical translation is short. There is no longer any such thing as a tax free relocation reimbursement, there is no coming date on which that changes, and every dollar of a relocation package is wages. It runs through payroll, it appears on the Form W-2, and it is supplemental wages under Publication 15, which lists "payments for nondeductible moving expenses" by name. If you promised a candidate $15,000 toward a move, you promised a net number, and a gross up is the only way to deliver it.

The federal divisor is only part of the answer. Nine states levy no tax on wage income at all, which makes the gross up arithmetic on this page complete on its own. Everywhere else a state rate goes into the divisor, and the state does not have to copy the federal structure when it sets one.

California is the instructive case because it does two things the federal rules do not. First, it splits supplemental wages into two categories with two different flat rates. Its Employer's Guide sets 10.23% for bonuses and stock options and 6.6% for other supplemental wages, naming overtime pay, commissions, sales awards, severance and vacation pay in the second group. A bonus and a severance check of identical size carry different California withholding.

Second, and this is the part that catches people, California removes the election in a specific case. The flat percentages apply only where the supplemental wage is not paid at the same time as regular wages. If it is paid together with the regular paycheck, the guide is directive rather than permissive: you are required to treat the sum as regular wages and withhold using the withholding schedules. Federal law leaves you the 22% election either way, subject to the prior withholding condition. California takes it away based purely on which payroll run you used.

So the same $10,000 bonus to the same California employee produces a different divisor, and therefore a different gross up, depending on whether payroll issued it as a separate check or folded it into the regular run. That is a scheduling decision made by whoever processes payroll, and it is quietly setting the cost of your bonus program.