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 method and the aggregate method. A third option, the annualized method, is used by some payroll systems for greater precision.

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 method is the most common because it's simple to administer — your payroll team applies one rate without needing to know your full-year income picture. However, it may not match your actual marginal tax rate. If you're in the 12% federal bracket, the flat rate over-withholds by 10 full percentage points.

Aggregate Method: Your employer adds your bonus to your most recent regular paycheck's gross wages, calculates withholding on the combined total, then subtracts what was already withheld on the regular paycheck. The difference is the bonus withholding amount. This method is more accurate to your actual tax situation but is more administratively complex.

Annualized Method: Your payroll system projects year-to-date income plus bonus to an annual figure, computes the annual tax, then backs out what's already been withheld year-to-date. The result is withholding that precisely accounts for where you are in the tax year — the most accurate method overall and most beneficial for mid-year bonuses received when year-to-date income is still relatively low.

Why the Method Matters for Your Take-Home

Consider two employees: one earns $40,000 per year (12% marginal rate) and one earns $120,000 per year (22% marginal rate). Both receive a $10,000 bonus. Under the flat rate method, both have $2,200 withheld in federal tax — the same amount regardless of their actual brackets.

Under the aggregate method, the lower-earning employee would have roughly $1,200 withheld — nearly $1,000 less than the flat rate takes. The higher earner would have approximately $2,200 withheld under aggregate, roughly matching the flat rate outcome. The practical result: the flat rate over-withholds substantially for employees in the 10% and 12% brackets.

This over-withholding is not a permanent loss — it becomes part of your tax refund when you file. But if you'd rather have that cash now rather than lending it to the government interest-free, asking your employer to use the aggregate method is worth exploring. IRS Publication 15 permits employers to use either method, and some payroll systems can accommodate the request.

FICA and State Taxes on Bonuses

Bonuses are fully subject to FICA taxes regardless of the withholding method used for federal income tax. Social Security at 6.2% applies on the first $176,100 of combined wages in 2025. Once you've reached that wage base across all your jobs, no additional Social Security is withheld on further earnings including bonuses. Medicare at 1.45% has no ceiling — it applies to every dollar you earn.

If your combined wages exceed $200,000 (single) or $250,000 (married filing jointly), an additional 0.9% Medicare surtax applies. This threshold is based on your total W-2 wages from all sources, not per employer, so bonuses that push you over the line trigger this extra tax on the amount above the threshold.

State bonus tax treatment adds another layer. Nine states have no income tax: Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, and Wyoming. States with income tax often apply a flat supplemental rate to bonuses distinct from their standard income tax brackets — California withholds 10.23% on bonuses under its supplemental wage rules, which can be significantly different from your effective state rate.

Strategies to Reduce Bonus Taxes

Defer to 401(k): Traditional 401(k) contributions made directly from your bonus reduce your federal and state taxable income dollar for dollar. The 2025 contribution limit is $23,500 ($31,000 if age 50+). If your bonus pushes you into a higher bracket, maximizing your 401(k) contribution can bring taxable income back down into a lower bracket — a meaningful permanent tax saving, not just a withholding deferral.

Request the Aggregate Method: If you're in the 10% or 12% federal bracket, the flat rate over-withholds significantly. Ask your HR or payroll department to use the aggregate method instead. They're permitted to use either approach — you just have to ask. Not all payroll systems support this request, but many do.

Consider Year-End Timing: If you have flexibility on when to receive your bonus, consider whether your income will be lower or higher next year. Receiving a bonus in a lower-income year (for example, if you plan to take unpaid leave or retire mid-year) reduces your effective rate. The Year-End Planner tab estimates whether your current withholding will result in a refund or a balance due at filing.

The Gross-Up Explained

A gross-up is when an employer wants you to receive a specific net amount after taxes rather than a specific gross amount. This is common with signing bonuses, relocation reimbursements, and some executive compensation arrangements. Instead of paying you $10,000 and letting you absorb the taxes, the employer calculates and pays enough gross to cover all your withholdings so you net exactly $10,000.

The math involves solving for the gross amount in reverse. If your combined effective withholding rate is 34.65% (22% federal + 7.65% FICA + 5% state), the gross-up formula is: gross = net / (1 − effective rate) = $10,000 / 0.6535 ≈ $15,305. The employer pays $15,305 gross, withholds $5,305 in taxes, and you receive $10,000 net.

Be aware that gross-ups create a tax-on-tax situation: the additional gross paid to cover taxes is itself taxable income, which is why the gross-up amount is always higher than it might seem at first glance. Our Scenario Analysis tab calculates the required gross for any net target using a binary search to account for this recursive effect precisely.