About the Bonus Tax Calculator
A bonus feels like free money until the paycheck arrives smaller than expected - bonuses are typically withheld at a flat federal rate that's often higher than your regular paycheck's rate. Our Bonus Tax Calculator shows what actually lands in your account.
How It Works
The IRS allows employers to withhold supplemental wages like bonuses at a flat 22% federal rate (for bonuses under $1 million) instead of using your regular W-4 withholding formula. The calculator applies that 22% flat rate plus standard FICA payroll tax to your bonus amount to estimate your net bonus payout.
Formula & Methodology
The IRS created the flat supplemental-wage withholding rate specifically because bonuses don't fit neatly into the regular per-paycheck withholding formula, which assumes a steady salary spread evenly across the year. Rather than trying to recalculate your entire W-4 withholding around a one-time payment, employers can simply withhold a flat 22% (or a higher flat rate above the $1 million threshold in a year) and let the difference between withholding and your true liability sort itself out when you file. This is why bonus paychecks often feel over-withheld - the flat rate doesn't know your actual marginal tax bracket.
Step-by-Step: Calculating It By Hand
- 1Start with the gross bonus amount.
- 2Multiply by 22% to find the flat federal withholding (for bonuses under $1 million in the year).
- 3Calculate FICA tax on the bonus the same way as regular wages (6.2% Social Security up to the cap, 1.45% Medicare).
- 4Subtract both the federal withholding and FICA from the gross bonus to find the net amount received.
Examples
Typical bonus
A $5,000 bonus → $1,100 federal withholding (22%) + $382.50 FICA = about $3,517.50 net.
Larger bonus
A $20,000 bonus follows the same flat rates → roughly $4,400 federal withholding + $1,530 FICA, netting about $14,070.
Advantages
- Explains why bonus withholding often looks higher than your regular paycheck's rate
- Separates the flat federal withholding from FICA payroll tax
- Helps you plan around the actual net amount rather than the sticker figure
- Useful for negotiating or timing bonus payouts
Common Mistakes
- Assuming the 22% flat withholding is your final tax rate - it's just what's withheld upfront
- Not realizing your actual tax liability on the bonus is reconciled (and can be refunded) when you file
- Forgetting bonuses over $1 million use a different, higher withholding rate on the excess
- Spending the full bonus amount before checking what's actually left after withholding
Edge Cases to Watch For
- Bonuses that push total supplemental wages over $1 million in a calendar year are withheld at 37% on the excess, not 22%.
- Some employers use the 'aggregate method' instead, combining the bonus with your regular paycheck and withholding based on your normal W-4 - this can produce a different (sometimes higher) withholding amount than the flat 22% method.
- The 22% withheld is not your final tax rate - if your actual marginal rate is lower, the excess comes back as part of your refund when you file.
- State supplemental wage withholding rates are separate from the federal 22% and vary by state, sometimes significantly.
Common Use Cases
- Estimating the real take-home amount from an upcoming bonus
- Understanding why a bonus paycheck's withholding looks unusually high
- Planning large purchases or savings goals around a net bonus figure
- Comparing bonus withholding against regular paycheck withholding