The offer letter said $30,000. The deposit was $19,605 — and a colleague who signed with a different health system kept even less of hers. Nothing was lost, and there is no special bonus tax. What happened is withholding: a payroll estimate of your eventual tax, applied under rules that do not know your actual bracket. The estimate reconciles on your Form 1040 the following spring, where the bonus is taxed at exactly the same as the rest of your income. Here is the full mechanism at 2026 numbers.
A sign-on bonus is supplemental wages, and payroll has exactly two ways to withhold on it
The IRS treats sign-on bonuses, relocation payments, retention bonuses, and most quality and productivity payouts as supplemental wages — compensation paid outside your regular salary. Under IRS Publication 15 (2026), your employer withholds federal income tax on supplemental wages by one of two methods, and the choice belongs to payroll, not to you.
| Method | How it works | Federal withholding on a $30,000 bonus |
|---|---|---|
| Optional flat rate | 22 percent of the payment, regardless of your W-4 or bracket | $6,600 |
| Aggregate method | The bonus rides inside a regular paycheck; the tables annualize the combined amount | Often $9,000 to $10,500 |
| Mandatory flat rate | Required on supplemental wages above $1,000,000 in a calendar year | 37 percent on the excess |
Most large hospital systems use the flat 22 percent rate because it is simple. The aggregate method shows up more often at smaller groups whose payroll software processes the bonus inside a regular check. Under aggregation, the withholding tables briefly treat you as someone who earns that combined paycheck every period of the year, so the marginal table rate — 32 or 35 percent for a typical attending check plus a bonus — applies to much of the payment. An aggregate-method bonus can shrink by 45 percent and still be processed correctly.
FICA applies on top, and the payment date decides how much
Neither method changes payroll taxes. Social Security tax of 6.2 percent applies to your first $184,500 of wages in 2026, Medicare tax of 1.45 percent applies to every dollar, and an additional 0.9 percent is withheld on wages above $200,000 in the year. A sign-on bonus paid in July, before your attending salary has crossed the wage base, takes the full 6.2 percent. The same bonus paid after your year-to-date wages pass $184,500 owes no Social Security tax at all — a $1,860 swing on $30,000 that depends entirely on the calendar.
Key insight
If the contract lets you pick the payment date and your base salary will cross the $184,500 wage base before year-end, a bonus paid after the crossing permanently avoids 6.2 percent Social Security tax on it. This is a real saving, not a timing shuffle — Social Security tax correctly withheld by a single employer is never refunded on your return.
The $30,000 check, line by line
Example calculation
Assumptions, stated explicitly: $30,000 sign-on bonus paid as a separate check in July under the optional flat rate; year-to-date wages below the Social Security base; an illustrative 5 percent flat state withholding; no retirement deferral applied to bonus pay.
Federal income tax withholding: $30,000 × 22% = $6,600.00 Social Security: $30,000 × 6.2% = $1,860.00 Medicare: $30,000 × 1.45% = $435.00 State income tax (illustrative): $30,000 × 5% = $1,500.00 Total withheld: $10,395.00 — 34.7 percent of the bonus Net deposit: $19,605.00
Where does the folk-wisdom 40 percent come from? Add a higher-tax state, a city wage tax, a or percentage election that applies to every eligible paycheck including bonuses, or the aggregate method, and total reductions of 40 to 47 percent are routine. Only part of that is tax, part may be your own retirement money, and none of it is final.
Withholding is an estimate; the tax settles at your marginal rate in April
The 22 percent flat rate is a withholding convention, not a tax rate. On your return, bonus dollars are ordinary income taxed at your marginal bracket — and for a typical first-year attending filing single, that bracket is higher than 22 percent.
Take a hospitalist earning a $280,000 base plus the $30,000 bonus, filing single with the $16,100 standard deduction under Rev. Proc. 2025-32. Taxable income is $293,900, inside the 35 percent bracket, which begins at $256,226 for single filers in 2026. Every bonus dollar is taxed at 35 percent: $10,500 of federal tax against $6,600 withheld, a $3,900 shortfall that surfaces on the return. The same physician married filing jointly on one income sits in the 24 percent bracket ($211,401 to $403,550), and the 22 percent withholding is nearly exact. Filing status, not the bonus, decides whether April brings a bill. How marginal brackets produce this result — and why your average rate stays far lower — is worked through in the tax brackets module.
Important
Flat 22 percent withholding systematically under-withholds for single attendings in the 32 and 35 percent brackets — a $3,000 to $3,900 gap on a $30,000 bonus. If your total withholding for the year misses the safe harbor (generally 90 percent of current-year tax, or 110 percent of prior-year tax once prior-year AGI exceeds $150,000), an underpayment penalty attaches. One line on Form W-4 Step 4(c) — extra withholding per paycheck — closes the gap.
Above $1,000,000 in supplemental wages, the 37 percent rate is mandatory
Once supplemental wages from an employer exceed $1,000,000 in a calendar year, Publication 15 (2026) requires 37 percent withholding on the excess, with no election available to you or to payroll. A first-year sign-on bonus does not get there alone, but stacked retention, relocation, and production bonuses in a senior contract can, and the rule applies to the combined total.
Quick takeaway
The bonus was never taxed at 40 percent. It was withheld at roughly 35 percent, part of the reduction may be your own retirement deferral, and the true tax — your marginal rate — settles at filing. The only live decision is whether to close a predictable under-withholding gap now through the W-4 or pay it as a lump sum in April.
Common questions
Can I ask payroll to withhold less than 22 percent on a bonus?
No. When the flat method is used, 22 percent is the floor set by Publication 15 (2026). You can add more through Form W-4 Step 4(c), but you cannot elect less. If the aggregate method over-withheld, the excess comes back as a refund at filing.
Is the bonus taxed again when I file?
No. Withholding is a deposit credited against your total tax. The return computes tax on all income at your brackets, subtracts everything already withheld, and the difference becomes the refund or the balance due. One tax, two timestamps.
How much should I set aside from the bonus for April?
If you file single and your taxable income lands in the 32 or 35 percent bracket, reserve 10 to 13 percent of the bonus — the spread between your marginal rate and the 22 percent already withheld. Married filing jointly at a typical single-physician income, often nothing.
What to do next
- Pull the paystub for the bonus payment. Federal withholding of exactly 22 percent means the flat method; anything else means aggregate.
- Project your 2026 taxable income — base plus bonus minus the $16,100 or $32,200 standard deduction — and find your marginal bracket.
- Multiply the bonus by the gap between that bracket and 22 percent. That number is your expected April shortfall or cushion.
- If there is a shortfall, either add it as extra per-paycheck withholding on Form W-4 Step 4(c) or park the cash in savings earmarked for April.
- Fold the result into your attending transition plan, and read the physician paycheck withholding guide before your first full attending paycheck arrives.
The first bonus check teaches the lesson every attending paycheck repeats: what lands in the account is an estimate, and the return is where the truth reconciles. The protocol above works with or without us. This is education, not individualized financial advice.