Receiving a bonus is exciting — until you see how much goes to taxes. The IRS classifies bonuses as supplemental wages, and how they're taxed depends on which withholding method your employer uses. Understanding this distinction can mean thousands of dollars difference in your paycheck.
The Three Bonus Withholding Methods
The IRS gives employers two primary methods to withhold taxes on supplemental wages: the flat rate (percentage) method and the aggregate method. A third option, the annualized method, is also used by some payroll systems.
Flat Rate Method: The IRS mandates a flat 22% withholding on supplemental wages up to $1,000,000 in 2025. For amounts above $1M in a year, the rate jumps to 37%. This is the most common method because it's simple to administer. However, it may not align with your actual marginal tax rate — if you're in the 12% bracket, the flat rate over-withholds significantly.
Aggregate Method: Your employer adds your bonus to your most recent regular paycheck's gross wages, then calculates the withholding on the combined total. They subtract what was already withheld on your regular paycheck, and the remainder is the bonus withholding. This method is more accurate to your actual tax situation but more administratively complex.
Annualized Method: Your payroll system projects your year-to-date income plus bonus to an annual figure, computes the annual tax, then backs out what's already been withheld. The result is withholding that precisely accounts for where you are in the tax year — the most accurate method overall.
Why the Method Matters
Consider two employees: one earns $40,000/year (12% marginal rate) and one earns $120,000/year (22% marginal rate). Both receive a $10,000 bonus. Under the flat rate, both have $2,200 withheld. Under the aggregate method, the lower-earning employee would have roughly $1,200 withheld — nearly $1,000 less. The higher earner would have approximately $2,200 withheld — same as the flat rate. The employee in the 12% bracket is substantially over-withheld under the flat rate.
FICA Taxes on Bonuses
Bonuses are fully subject to FICA taxes regardless of the withholding method. Social Security tax (6.2%) applies on the first $176,100 of combined wages in 2025. Once you've hit that wage base across all jobs, no additional Social Security is withheld. Medicare tax (1.45%) has no ceiling. If your combined wages exceed $200,000 (single) or $250,000 (married filing jointly), an additional 0.9% Medicare surtax applies.
State Taxes on Bonuses
State bonus tax treatment varies widely. Nine states have no income tax at all: Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, and Wyoming. Several states with income tax apply a flat supplemental rate distinct from the standard rate — California, for example, withholds 10.23% on bonuses under its supplemental wage rules rather than the standard income tax rate. Our calculator uses standard state income tax rates as a conservative estimate.
Strategies to Reduce Bonus Taxes
1. Defer to 401(k): Contributions to your traditional 401(k) directly from your bonus reduce your federal and state taxable income. The 2025 contribution limit is $23,500. If your bonus pushes you into a higher bracket, maximizing your 401(k) contribution can bring you back down.
2. Request the Aggregate Method: If the flat rate over-withholds (common for lower earners), ask your HR or payroll department to use the aggregate method. They're permitted to use either — you just have to ask.
3. Timing Bonuses Across Year-End: If you have flexibility on when to receive your bonus, receiving it in a low-income year (if you expect income to drop) can reduce your effective rate. Conversely, pushing it to next year might help if you plan significant deductions.
4. Understand Over-Withholding: Over-withheld bonus taxes aren't lost — they become part of your tax refund when you file. But that money is essentially an interest-free loan to the government. The Year-End Planner tab estimates whether you'll owe or get a refund.
The Gross-Up
A gross-up is when an employer wants you to receive a specific net amount — perhaps a $10,000 net signing bonus. They gross up the payment by paying enough extra to cover all your taxes. For a 22% federal + 7.65% FICA + 5% state situation (total ~34.65% effective rate), they'd need to pay roughly $15,300 gross for you to net $10,000. Our Scenario Analysis tab calculates this precisely using a binary search algorithm.