If your bonus was taxed at 40% and roughly that much disappeared before it reached your account, two things had to be true at once. Your employer used the aggregate method, and your bonus was large compared with your salary. Either one alone does not get you to 40%. Together they do, and the good news is that most of the difference is not tax you owe.
The short answer
There are two legal ways to withhold from a bonus, and they behave completely differently.
The percentage method taxes the bonus on its own at a flat 22% federal, plus 7.65% for Social Security and Medicare. That is 29.65%, and it does not move. Not with your salary, not with the size of the bonus. A $5,000 bonus and a $25,000 bonus are both withheld at 29.65%.
The aggregate method adds the bonus to a regular paycheck and withholds as though you are paid that much every single period. This is where 40% comes from, because a one-off payment gets treated as a permanent raise.
Flat-rate withholding on a bonus
22% federal + 7.65% FICA = 29.65%
Fixed at every salary and every bonus size · state supplemental tax is charged on top
Why the aggregate method reaches 40% and the flat one never does
The aggregate rate depends entirely on how big the bonus is next to your salary. Here is the same comparison at four different sizes, all in a state with no income tax:
- $5,000 bonus on a $65,000 salary: flat 29.65%, aggregate 30.66%. A difference of just $50.
- $10,000 on $65,000: flat 29.65%, aggregate 35.06%. A difference of $541.
- $20,000 on $120,000: flat 29.65%, aggregate 40.26%. A difference of $2,122.
- $25,000 on $95,000: flat 29.65%, aggregate 40.51%. A difference of $2,715.
Notice what stays still. The flat method is 29.65% in all four rows. Only the aggregate rate climbs, and it climbs because adding $25,000 to a single biweekly paycheck makes that paycheck look like a salary of roughly $740,000 a year to the withholding table. The table charges accordingly, then your next paycheck goes back to normal.
This is the part worth holding onto. Nothing above changed what you owe. Withholding is a prepayment, not a separate tax on bonuses. Your bonus is taxed at exactly the same rates as the rest of your income when you file, and if too much was taken it comes back as a larger refund.
Working out which method your employer used
You can tell from the pay stub without asking anyone.
Take the federal income tax withheld from the bonus and divide it by the gross bonus. If you get almost exactly 22%, that is the percentage method. Anything meaningfully above it, and they aggregated.
Two practical notes. The 22% is federal income tax only, so exclude the Social Security and Medicare lines from that division or the number will look wrong. And if the bonus was paid on the same check as your regular wages rather than on its own, that is a strong sign of aggregation, since the percentage method usually means a separate payment.
Which payments get withheld this way
A bonus is not the only thing treated as supplemental wages. The same two methods apply to commissions, severance, back pay, accumulated sick leave paid out, prizes and awards, retroactive raises and certain overtime arrears.
That is worth knowing because it explains the other case where people find a bonus taxed at 40%: someone leaving a job who receives severance and a final vacation payout in the same period. Those stack, and a single check carrying several months of value annualizes into a very large notional salary indeed. If that is where you are, how much of a PTO payout you keep runs the same two methods over a leave balance and covers whether you are owed one at all.
The rate that is not your employer's choice
One threshold overrides everything above. Once the supplemental wages you have been paid in a calendar year pass $1 million, the rate on the excess becomes 37% and your employer no longer has any discretion. Below that line, the method is theirs to pick.
When the bonus is paid changes the answer too
Under the aggregate method the bonus is combined with whatever regular pay shares that period, so the pay cycle matters more than it should.
A bonus paid on its own, in a period with no regular wages, annualizes from a smaller base than one paid alongside a full paycheck. A bonus split across two periods annualizes from a smaller base again. None of this changes your tax, only how much is fronted, but it is why two colleagues with identical bonuses can see different percentages.
Your state takes its own cut on top
Every figure above is federal plus FICA. Most states apply their own flat supplemental rate to bonuses, and it is charged separately.
On a $10,000 bonus, California adds $880 and New York adds $540. So the same bonus that leaves $7,035 in Texas leaves about $6,155 in California. If your effective rate looks higher than the numbers in this article, your state is usually the reason.
What you can actually do about it
Not much about the method, honestly. It is a payroll configuration and rarely changed for one employee. But there are three things worth doing. The same withholding quirk shows up on overtime, for the same reason: a big week is withheld as though every week looked like that one.
Ask before the bonus is paid, not after
Payroll can tell you which method they use. Knowing in advance turns an unpleasant surprise into a number you planned around, which matters if the bonus was earmarked for something.
Consider a pre-tax contribution
Some employers let you direct part of a bonus into a 401(k) or HSA. That reduces the taxable amount rather than just the withholding, so it changes what you owe as well as what is taken. Ask whether a bonus deferral election is available, and note that it usually has to be made before the payment.
Check your W-4 if this happens every year
If you receive a large bonus annually and get a big refund every spring, you are lending money interest-free for a year. Reducing withholding on your regular paychecks rebalances that. The reverse is also true: if the bonus left you short in April, extra withholding on your regular pay is the fix.
To see both methods side by side on your own numbers, the bonus tax calculator runs them together and lets you switch between them. Commissions, severance, back pay and prizes are all withheld the same way, so it works for those too.
Compare both methods on your own bonus
Frequently asked
Because your employer used the aggregate method and the bonus was large relative to your salary. A $25,000 bonus on a $95,000 salary withholds about 40.5% that way, against 29.65% under the flat method. The difference is withholding, not tax owed, and returns as a refund.
No. A bonus is taxed at your normal rates when you file. It is withheld differently, either at a flat 22% federal plus 7.65% FICA, or by treating one paycheck as though you earned that much every period, which takes more.
If more was withheld than you owe for the year, yes, as part of your refund. Withholding is an advance payment against your final bill, so over-withholding on a bonus is money returned rather than money lost.
About $7,035 under the flat method in a state with no income tax. Under the aggregate method on a $65,000 salary it is closer to $6,494. In California expect around $6,155, since the state adds its own supplemental rate.
You can ask, though it is usually a payroll system setting rather than a per-employee choice. Both methods are legal and the employer decides. Asking which one they use before the bonus is paid is more useful than asking them to change it.