Illinois Bonus Tax Calculator

When a bonus is paid on its own paycheck, Illinois employers normally withhold about 34.6% in total: the federal flat supplemental rate of 22%, Illinois income tax at 4.95%, Social Security at 6.2% and Medicare at 1.45%. A $5,000 bonus therefore arrives as roughly $3,270. This is a withholding rate, not the final tax — the bonus is ordinary income on your return, so if 22% overshoots your real federal bracket the difference comes back as a refund.

No. There is no special bonus tax rate in Illinois or federally. What exists is a special withholding rule for supplemental wages, which lets an employer take a flat 22% for federal tax instead of running the bonus through your Form W-4 tables. Illinois does not even do that — the state has no separate supplemental rate, so a bonus is withheld at the same flat 4.95% as your salary. At filing time every dollar is treated identically.

The percentage method applies when the bonus is paid separately from regular wages: the employer withholds a flat 22% federal on the bonus alone. The aggregate method applies when the bonus is combined with regular wages on one paycheck: the employer adds the two together, runs the total through your Form W-4 withholding tables, subtracts what would normally be withheld on the regular wages, and the remainder is the bonus withholding. The aggregate method usually withholds more from a large bonus because the combined paycheck annualizes into a high bracket. Switch between the two above to see the difference on your own figures.

Almost always the aggregate method plus a 401(k) deferral. If the bonus rode on a regular paycheck, payroll annualized the combined amount — a $10,000 bonus on a bi-weekly paycheck looks, for that one calculation, like a $260,000 salary — and withheld at a bracket you will never actually pay. Add a 401(k) percentage that applies to bonuses and the deduction can easily reach 40%. None of it is lost; the over-withholding is settled when you file. If it happens every year, adjusting Step 4(b) of your Form W-4 is the fix.

Under the flat percentage method, a $10,000 bonus has $2,200 withheld for federal tax, $495 for Illinois, $620 for Social Security and $145 for Medicare — leaving $6,540. Under the aggregate method the amount withheld depends entirely on your regular pay, your filing status and your dependents, and is usually higher. Either way, your real tax on the bonus is settled on your return, not on the pay stub.

You can defer as much of it as your plan allows, up to the annual elective deferral limit across all your contributions for the year. A traditional deferral removes the bonus from federal and Illinois income tax withholding entirely — but not from FICA. Social Security and Medicare still take 7.65% of the deferred amount, because FICA applies to gross wages regardless of retirement deferrals. Many plans also apply a separate bonus deferral election, so check the plan rules before assuming your regular percentage carries over.

Yes. The IRS treats commissions, overtime paid separately, severance, back pay, accumulated sick leave payouts, prizes, awards and retroactive pay increases all as supplemental wages, subject to the same 22% flat withholding option. Illinois applies its flat 4.95% to all of them without distinction. One exception worth knowing: if your total supplemental wages for the year exceed $1 million, the excess must be withheld at 37% and the employer has no choice in the matter.

In Box 1 with your regular wages, not on a separate line — a bonus is simply wages. It also appears in the Social Security and Medicare wage boxes, and the tax withheld is folded into Boxes 2, 4, 6 and 17. If you need to see the bonus on its own, the pay stub for the period it was paid is the only place it is broken out.