How Bonus Taxation Actually Works: What Payroll Does vs. What You Owe
The most common source of confusion about bonus taxes comes from conflating withholding with liability. Your employer withholds taxes from your bonus according to IRS rules — but your actual tax bill on that bonus is determined by your total income when you file your return. These are two different numbers, and understanding the gap between them is the single most useful thing this page can teach you.
How Bonus Size Affects What You Keep
The table below shows net bonus at five salary levels using the flat 22% method for a single filer in 2026 — including federal, FICA, and a representative 5% state rate. The "keep rate" reveals a pattern most bonus recipients overlook: mid-range earners often lose more in total withholding as a percentage than very high earners, because the 22% flat rate under-withholds at the top and over-withholds at the bottom.
| Base Salary | Bonus | Federal (22%) | FICA | State (5%) | Total Withheld | Net Bonus | Keep Rate |
|---|---|---|---|---|---|---|---|
| $50,000 | $5,000 | $1,100 | $383 | $250 | $1,733 | $3,268 | 65.4% |
| $85,000 | $10,000 | $2,200 | $765 | $500 | $3,465 | $6,535 | 65.4% |
| $130,000 | $20,000 | $4,400 | $1,530 | $1,000 | $6,930 | $13,070 | 65.4% |
| $180,000 | $30,000 | $6,600 | $709 | $1,500 | $8,809 | $21,191 | 70.6% |
| $250,000 | $50,000 | $11,000 | $1,175 | $2,500 | $14,675 | $35,325 | 70.7% |
The two withholding methods, compared
The IRS gives employers a choice: use a flat 22% rate on the bonus amount (called the "percentage method" for supplemental wages), or combine the bonus with the employee's regular paycheck and run the entire combined amount through the standard withholding tables (the "aggregate method"). The flat method is simpler for payroll to process and gives you a predictable withholding. The aggregate method recalculates your tax as though you earn that combined amount every pay period — which can significantly overstate your bracket for a single paycheck.
Consider a single filer earning $85,000 per year (about $3,269 per biweekly paycheck). If they receive a $10,000 bonus on the same check, the aggregate method treats the check as though the employee earns $13,269 biweekly — or roughly $345,000 annualized. That pushes the withholding calculation into the 24%–32% range for the period, even though their actual annual income is $95,000. The result: the aggregate method may withhold $800–$1,200 more in federal tax than the flat method on a $10,000 bonus. You eventually get this back at filing time, but the cash-flow impact can last months.
| Factor | Flat 22% Method | Aggregate Method |
|---|---|---|
| How federal tax is calculated | 22% of the bonus (or 37% above $1M) | Bonus + regular pay run through wage bracket tables as one combined check |
| Who decides which to use | Your employer, not you | Your employer, not you |
| Typical over/under-withholding | Under-withholds for 24%+ bracket earners; over-withholds for 10–12% bracket | Almost always over-withholds; can significantly overstate bracket |
| FICA treatment | Same: SS + Medicare on full bonus amount (subject to caps) | Same: SS + Medicare on full bonus amount (subject to caps) |
| Best for earners in… | 22% bracket (accurate withholding); also preferred by lower-bracket earners (less over-withholding than aggregate) | Rarely beneficial upfront — may cause less of a surprise at filing if your rate is above 22% |
The Social Security wage base — the hidden variable
Social Security tax stops at a set annual earnings threshold: $176,100 in 2025 and $184,500 in 2026. If your regular salary has already pushed you past the cap by the time your bonus arrives (typically in Q4 for calendar-year bonuses), no additional Social Security tax applies to the bonus — saving you 6.2% on every dollar. For someone earning $190,000 with a $20,000 bonus paid in December, the entire bonus escapes Social Security tax. But if the same bonus were paid in March, with only $47,500 in YTD wages at that point, the full $20,000 bonus is subject to the 6.2% charge — a $1,240 difference purely from timing.
This interaction is why the calculator asks for both your annual salary and the month your bonus is paid: it estimates your year-to-date earnings to determine how much of the bonus falls above or below the Social Security wage base cap.
Additional Medicare Tax at higher incomes
Employers must withhold an extra 0.9% Medicare surtax once an employee's wages exceed $200,000 in a calendar year (this threshold applies regardless of filing status at the employer level). The actual liability threshold differs by filing status — $250,000 for married filing jointly, $125,000 for married filing separately — but employers don't account for your spouse's income. This means the withholding threshold and the liability threshold may be different, creating a mismatch that only resolves on your return. For a dual-income married couple each earning $160,000, neither employer withholds the surtax — but the couple owes it on the combined $320,000. If either receives a $20,000 bonus, the Additional Medicare Tax on that bonus amount ($180 at 0.9%) is not withheld and will show up as tax owed at filing.
Withholding vs. actual liability: the real math
The flat 22% withholding is a convenience for payroll — not a reflection of your real tax rate. Here's how the numbers play out at filing time for three different earners:
Strategies that actually affect your net bonus
Redirect to 401(k): If your employer allows you to specify a separate 401(k) contribution rate for bonuses, directing a portion (or all) of your bonus pre-tax avoids both federal and state income tax withholding. FICA still applies to the full gross bonus. On a $10,000 bonus for someone in the 24% bracket with a 5% state rate, routing $5,000 to 401(k) reduces combined income tax withholding by approximately $1,450 — and the money compounds tax-deferred.
Timing matters for SS cap: If your salary is close to the Social Security wage base, asking your employer to pay the bonus later in the year (after you've exceeded the cap) can save up to 6.2% on the portion that falls above the limit. On a $20,000 bonus, that's up to $1,240.
Adjusting W-4 is risky: Temporarily increasing allowances to reduce withholding on the bonus paycheck is a widely cited tip, but it affects every paycheck until you change it back. If you forget, or if payroll processes the change slowly, you could end up under-withheld for the rest of the year. This approach requires discipline and precise timing.
What changes in 2026 under OBBBA
The One Big Beautiful Bill Act (signed July 2025) permanently extends the TCJA rate structure: seven brackets from 10% to 37%, and the flat 22% supplemental withholding rate. The $1M threshold for the 37% supplemental rate is not indexed for inflation before 2027. The 2026 Social Security wage base rises to $184,500 (from $176,100 in 2025) — meaning the FICA "escape point" for year-end bonuses shifts higher. Standard deductions also increase ($16,100 single / $32,200 MFJ), slightly reducing taxable income across all scenarios.
Common mistakes that cost money (or cause panic)
Mistake #1: Thinking your bonus is taxed at a separate, higher rate. The IRS does not have a "bonus tax rate." Bonuses are ordinary income taxed at your marginal rate. The 22% is a withholding convenience, not a final tax. If your marginal rate is 12%, you are over-withheld. If it's 32%, you are under-withheld. In both cases the reconciliation happens on your return.
Mistake #2: Ignoring FICA on the bonus. Many people focus on the 22% federal withholding and forget that Social Security (6.2%) and Medicare (1.45%) also apply. Combined with a 5% state rate, total withholding on a bonus can exceed 34% — even before reaching the 24% federal bracket. The "surprise" is the FICA layer, not the income tax rate.
Mistake #3: Comparing bonuses across states without adjusting for FICA cap. An employee earning $180,000 in Texas (no state income tax) with a December bonus doesn't owe Social Security on the bonus — their salary already exceeded the cap. An employee earning $70,000 in California with the same December bonus owes both 6.2% SS and California's high state rate. The net difference for a $15,000 bonus can exceed $2,500, and most of it is driven by the FICA cap interaction, not just the state rate.
Mistake #4: Spending the "refund" before it arrives. If the aggregate method over-withholds by $1,500 on a March bonus, that money is locked up until you file in the following April — potentially 13 months of lost opportunity. At a 5% savings rate, the time value of that over-withholding is $65–$75. Not devastating, but worth knowing when comparing job offers that include annual bonuses.