Bonus Tax Calculator Step-by-Step (2026): Walk Through Every Line

Most online bonus calculators show you one number and a pie chart. That works if you trust the inputs and never need to defend the math to anyone — your spouse, your accountant, the angry version of yourself who is going to look at the paystub in three days. This article does it the slow way: six numbered steps from gross bonus to net deposit, with the rules and rates spelled out at each one, plus three worked examples ($5,000, $20,000, $250,000) across a no-tax state, a mid-tax state, and California. Plug your own number into the bonus tax calculator when you want the answer instantly; read this when you want to understand how the answer is produced.

Step 1: Start with the Gross Bonus

Gross is the headline number — the amount your employer told you the bonus is for. For percentage-method withholding (the more common case), this is also the wage base unless you have a 401(k) deferral set to include bonuses. For the aggregate method, the bonus is combined with your regular check first, then the whole thing is run through normal withholding tables as though it were a single annualized pay period.

Worked example A: $5,000 spot bonus.
Worked example B: $20,000 year-end annual bonus.
Worked example C: $250,000 retention bonus.

Step 2: Apply Pre-Tax 401(k) and HSA Deferrals (If Any)

This step matters because pre-tax deferrals reduce the wage base on which everything else is calculated. Many 401(k) plans include bonus pay in the deferral base by default; some plans require a separate bonus deferral election; some plans exclude bonuses entirely. Check your Summary Plan Description or ask payroll.

If the plan includes the bonus and your deferral rate is 10%, then a $5,000 bonus sends $500 to your traditional pre-tax 401(k) before tax is calculated. The wage base for federal, FICA, and state withholding becomes $4,500. The same logic applies to HSA pre-tax payroll deductions (limited to $4,300 single / $8,550 family in 2026).

Roth 401(k) contributions do not reduce the tax base. They come out of post-tax dollars in Step 6.

For all three worked examples below we will assume no 401(k) bonus deferral so the gross equals the wage base. See our Roth vs traditional 401(k) explainer if you are deciding which to use.

Step 3: Federal Supplemental Withholding

The 2026 rule comes from IRS Publication 15 and Treas. Reg. § 31.3402(g)-1:

• Percentage method: 22% flat on the first $1,000,000 of cumulative YTD supplemental wages from one employer in one calendar year. 37% flat on anything above $1M.
• Aggregate method: bonus is combined into a regular paycheck and withheld using normal income tax tables, treating that single paycheck as though it were a typical pay period for the year.

We cover the difference in depth in the aggregate vs percentage method explainer. For the worked examples here we will use the percentage method, which is the more common employer choice for clearly labeled bonus payments.

The $250,000 example assumes the executive has already crossed $800K in YTD supplemental wages, so $200K of the new bonus stays under the $1M cap (22%) and $50K spills into the 37% bracket. See the 22% vs 37% supplemental rate breakdown for the cumulative-counting rule in detail.

Step 4: Apply FICA (Social Security + Medicare)

FICA is two separate taxes that ride along on every bonus regardless of state:

• Social Security: 6.2% on wages up to the 2026 wage base of $168,600. Above that, Social Security stops withholding for the rest of the calendar year.
• Medicare: 1.45% on all wages with no cap.
• Additional Medicare Tax: 0.9% on wages above $200,000 (employer is required to start withholding once any single employee crosses $200K YTD, regardless of marital status — the surtax is reconciled at filing).

Step 5: State Supplemental Withholding

Each state runs its own supplemental withholding rule. Seven states have no income tax at all — Alaska, Florida, Nevada, South Dakota, Tennessee, Texas, Wyoming. New Hampshire and Washington tax only narrow categories that do not include wages. California has the highest supplemental rate (10.23% for bonus and stock-option wages, 6.6% for other supplemental wages). New York applies a flat 11.7% New York City resident rate plus 9.65% state for high earners.

The state-by-state supplemental rate table covers all 50; here we use three representative states for the worked examples.

Step 6: Subtract Post-Tax Deductions and Get the Net

Post-tax deductions — Roth 401(k), Roth IRA payroll deferrals, post-tax health insurance, group-term life premiums above $50K, garnishments, union dues — come out after withholding has already been calculated. For our worked examples we will assume none, which makes the net deposit just gross minus all taxes from Steps 3–5.

The pattern is consistent: 60–70% net is the realistic banding for a typical bonus once federal supplemental, FICA, and state withholding have been applied. If your paystub is way outside that range, something is unusual — either the aggregate method is in play (often produces higher withholding), a 401(k) bonus deferral is shrinking the wage base, or YTD wages have crossed one of the bracket cliffs (Social Security cap at $168,600, additional Medicare surtax above $200K, federal 37% supplemental above $1M).

Worked Example Summary

Three identical-gross-but-different-net scenarios show why the headline withholding rate alone tells you very little:

• $5,000 spot bonus, Texas: $3,517.50 net (70.4%). The cleanest scenario — no state tax, no FICA surtax, no $1M issue. This is the upper bound for typical bonuses.
• $5,000 spot bonus, California: $3,006.00 net (60.1%). California's 10.23% supplemental rate alone strips $511.50 — almost two-thirds of one extra month's grocery budget for a household earning $80K.
• $20,000 annual bonus, New York: $12,788 net (63.9%). The mid-tier scenario. A 36% effective withholding rate that converts to roughly a 28% real tax bill at filing for a typical $120K earner.
• $250,000 retention bonus, California: $156,050 net (62.4%). The 37% federal supplemental rate kicks in on $50K of this bonus and the 0.9% Medicare surtax hits the full $250K — but the Social Security 6.2% disappears entirely above the $168,600 cap, partially offsetting.

The Calculator Shortcut

The PayScale Pro bonus tax calculator runs all six steps and shows the answer instantly, with the wage base, federal supplemental rate, FICA, and state withholding broken out by line. Use it as the fast path. Read this article when you want to debug a paystub that does not match the calculator — typically because of a 401(k) bonus deferral, an aggregate-method employer, or a Social Security cap crossing mid-year.

Two related calculator scenarios that follow the same six-step framework but adjust the inputs: the why my bonus feels smaller in 2026 walkthrough and the spot vs annual bonus comparison. For the broader supplemental wage framework, see the 2026 supplemental wages reference.

What the Calculator Does Not Tell You

Withholding is not the same as final tax. A $5,000 spot bonus withheld at 22% federal supplemental can produce a refund at filing if your real marginal rate is 12%, or trigger a tax bill if your real marginal rate is 32%. The percentage method is an estimate the IRS picked as a midpoint convenience — it is not a forecast of your actual liability.

If you receive irregular large bonuses and you are concerned about under-withholding, the cleanest fix is to update your W-4 mid-year with an additional withholding amount (Step 4(c) on the form). This adds a flat dollar amount to every paycheck's federal withholding regardless of whether the percentage or aggregate method was applied to the bonus itself. For the broader take-home picture see the take-home pay calculator.

Bottom Line

Six steps: gross → 401(k)/HSA → federal supplemental → FICA → state → post-tax. Every legitimate bonus calculator in the US runs that sequence. The reason the same gross bonus produces wildly different net deposits is which line items apply in each step, not different math. Plug your number into the PayScale Pro bonus tax calculator for the answer. Walk through the steps above when the answer surprises you and you need to know why. For the broader fitness-and-energy-budget side of personal math, our sister site has a parallel BMR formula explainer in exactly this style.