Illinois Bonus Tax Calculator 2026
Illinois lets employers withhold a bonus at the 4.95% income tax rate in effect on the payment date.
Bonus check calculator
The rule in the Illinois Administrative Code
Illinois sets its bonus rule in 86 Ill. Adm. Code 100.7050(c). Supplemental wages "such as bonuses, commissions, and overtime pay" are withheld under "the same methods provided for withholding on those wages under the Internal Revenue Code," but "an employer may elect to compute the amount of tax to be withheld using the tax rate in effect for the date the compensation is paid." That rate is 4.95% — the figure printed on the cover of Booklet IL-700-T, Illinois Withholding Tax Tables, effective January 1, 2026. A $5,000 bonus carries $247.50; a $12,000 bonus, $594.00.
Why the method barely matters here
Illinois taxes income at a single rate, so the two routes the rule allows converge. Regular-wage withholding subtracts $2,925 per IL-W-4 allowance (plus $1,000 per additional allowance on line 2) and multiplies the rest by 4.95%; once regular pay has used those allowances, a bonus added to it adds 4.95% of the bonus either way. Pre-tax 401(k) deferrals reduce Illinois withholding too: deferring 6% of the bonus brings the Illinois line to $232.65.
| Rule | 4.95% (the rate in effect on the payment date) |
|---|---|
| Valid through | No end date in the governing text |
| Documents | 86 Ill. Adm. Code 100.7050(c) and Booklet IL-700-T (2026) (IL-700-T effective January 1, 2026 (R-12/25)) |
| Agency | Illinois Department of Revenue |
| Federal income tax | −$1,100.00 |
| Social Security | −$310.00 |
| Medicare | −$72.50 |
| Illinois income tax | −$247.50 |
| Net | $3,270.00 |