The flat rate is a shortcut, not your tax rate
Running your bonus through the W-4 tables would withhold based on your filing status and dependents — accurate but slow. The percentage method's flat 22% approximates a middle-bracket worker. If your marginal bracket is 12%, the flat rate takes nearly double what you'll owe; at 32%, it under-withholds and April brings a bill.
FICA and state stack on top
7.65% FICA comes off every bonus dollar (unless you've passed the Social Security wage base). State withholding adds 0%–10.23%. The perceived 'tax' on a bonus is usually this stack — 30–40% — compared with perhaps 18–22% net effective withholding on your regular check.
How the money comes back
- At filing: your W-2 adds the bonus to wages once; the tax computed on your actual bracket determines what was over-withheld.
- Mid-year: a W-4 update can reduce withholding on later regular checks to compensate.
- Pre-tax deflections: 401(k), HSA or FSA elections applied to the bonus shrink the taxable base before withholding runs.
When a bonus genuinely costs more tax
In a year where the bonus pushes you across a bracket threshold, the margin — only the dollars above the line — is taxed higher than it would have been alone. That's real extra tax, but it's marginal and usually small; the feeling of 'they took 40%' is almost always withholding, not liability.