How the Illinois Flat Income Tax Works
Illinois levies a single flat rate of 4.95% on taxable income for every filer, from the first dollar of a part-time wage to a seven-figure salary. The rate has held at 4.95% since 2017, and voters rejected a move to graduated brackets in November 2020, leaving the flat structure locked into the state constitution. Your marginal rate and your top rate are the same number, and a raise never pushes part of your income into a higher state bracket.
With no brackets to climb, the only inputs that change your state bill are income, exemptions, and credits. Overtime pay, bonuses, and commissions are all taxed at the same 4.95% once they land in your federal AGI — if you want to model a heavier overtime schedule before estimating the tax on it, the Illinois overtime calculator works out the gross-up first.
The state also does not let cities piggyback an earnings tax. Unlike Ohio or Pennsylvania, where municipal income taxes commonly add 1-3% on top of state tax, an Illinois worker pays 4.95% in Chicago, Peoria, or a farm town. Only the sales tax side varies widely by address, with Chicago's combined rate reaching 10.25%. Owners of S-corps and partnerships can also elect the 4.95% pass-through entity tax at the business level, which sidesteps the federal deduction cap on state income taxes — a planning move worth raising with a CPA once profits clear six figures.
Personal Exemptions and Dependents
The flat rate applies after exemptions, and for tax year 2024 each exemption is worth $2,775. You get one for yourself, a second for a spouse on a joint return, and one for every dependent claimed. A married couple with two kids starts with $11,100 shielded from the 4.95% rate before any other adjustments enter the picture.
At 4.95%, each exemption knocks $137.36 off the state bill (2,775 × 0.0495). The exemption had been frozen at $2,425 after inflation indexing was suspended in 2020, then jumped for 2024 when indexing resumed, so older worksheets quote a lower figure — always verify against the current IL-1040 instructions before filing.
Taxpayers who are 65 or older or blind can claim an additional exemption on top of the personal ones, and married spouses filing separately each claim their own exemption on their returns. If you live in Illinois but work across the border, reciprocal agreements with Iowa, Kentucky, Michigan, and Wisconsin keep you from being taxed twice on the same wages.
The Illinois Property Tax Credit
Homeowners get a credit equal to 5% of the property tax paid on their principal residence, taken directly off the state income tax calculated on the IL-1040. With Illinois carrying some of the highest property tax bills in the country — the median household pays around $4,700 a year — the typical credit lands near $235.
The credit is nonrefundable: it can zero out your state tax but never below zero, which matters for low-income filers whose 4.95% liability is smaller than the credit itself. Renters do not qualify for this credit; it is reserved for the person or couple legally liable for the property tax bill. Parents paying private or parochial school tuition should also note the separate K-12 education expense credit — 25% of qualifying expenses above $250, worth up to $750 — which stacks on top of the property tax credit on the same return.
To claim it, you must have been liable for the tax and actually paid it during the tax year — prorated bills from a mid-year home purchase count only for the portion you paid. Keep the second-installment receipt or county tax letter, because the Illinois Department of Revenue routinely matches claimed credits against county records.
From Gross Income to Illinois Taxable Income
Illinois starts from federal AGI, which is why the calculator subtracts pre-tax retirement contributions before applying the flat rate. Money funneled into a traditional 401(k), a 403(b), or a health savings account never appears in the base, so it escapes the 4.95% entirely — the same mechanics that drive the adjustments walked through in the AGI calculator.
From that base, Illinois allows subtractions that shrink taxable income further: federally taxable Social Security, IRA and pension distributions, and interest on Illinois municipal bonds all come back off. Additions include interest from other states' municipal bonds and certain pass-through entity adjustments reported to you.
Federal payroll taxes run in parallel and are not deductible against Illinois tax for most filers. For the combined withholding picture — 7.65% FICA plus 4.95% state plus federal brackets — model the payroll layer with the FICA tax calculator before committing to a salary number in negotiations.
Retirement Income Is Subtracted
Illinois is one of a handful of states that effectively does not tax retirement income. Distributions from 401(k) plans, IRAs, pensions, and profit-sharing plans are subtracted on Schedule M, so the practical state rate on a retiree's core income is 0%.
That makes the state unusually friendly to retirees with large deferred accounts — a couple drawing $80,000 from traditional IRAs owes Illinois nothing on those withdrawals, though federal tax still applies and Required Minimum Distribution rules still force the payouts. Working retirees should still model withdrawal sizing with a savings goal calculator when deciding how much to convert to Roth each year.
Note the boundary: wages earned after retirement age are fully taxed at 4.95%, and a post-retirement job's salary does not qualify for the subtraction. Only plan distributions, pension payments, and Social Security come off the base. Military retirement pay gets the same treatment, which is why Illinois routinely ranks alongside the states veterans choose for retirement; the subtraction covers uniformed service pensions in full with no dollar cap.
How Illinois Compares to Neighboring States
Among neighbors, Illinois sits in the middle of the pack. Indiana's flat rate has fallen to roughly 3.0%, Michigan charges about 4.0% flat, Missouri runs progressive brackets topping out near 4.8%, and Wisconsin's top bracket reaches 7.65%. Rates shift nearly every year, so treat any comparison as directional rather than permanent.
A single filer earning $100,000 owes about $4,281 to Illinois after typical exemptions and the property tax credit. The same earner in Wisconsin's upper brackets can owe noticeably more, while an Indiana earner owes less in absolute terms on the lower flat rate. For states with bracket structures, run a purpose-built tool such as the California tax calculator or the Alabama tax calculator to apply the right deductions.
The flat structure is the real draw for high earners: a $400,000 salary pays the same 4.95% marginal rate as a $40,000 one, and the effective rate never climbs the way it does in graduated states. For lower incomes the math reverses, since states with large standard deductions or refundable credits can zero out tax that Illinois still collects on the first dollar after exemptions.
Effective Rate and Take-Home Pay
Because exemptions are fixed dollar amounts, your effective state rate rises with income even though the marginal rate never moves. At $75,000 with the default inputs here, the effective rate lands at 4.45%; at $150,000 it reaches about 4.70%, creeping toward the 4.95% ceiling as income grows.
For paycheck planning, the state slice is small next to federal withholding and FICA, but it is real money: $3,201 a year on the default scenario is $267 a month. The disposable income calculator stacks the state layer on top of federal tax for a full take-home view.
Salaried employees should sanity-check the Illinois withholding line on each pay stub — the IL-W-4 allowances you filed drive it, and stale allowances after a marriage, divorce, or new baby leave you owing in April. A biweekly pay calculator spreads the corrected annual figure across 26 checks.
Using the Results for Planning
Self-employed filers owe this number in quarterly installments — roughly $800 a quarter on the default $3,201 estimate — with due dates in April, June, September, and January. Illinois accepts your estimate if it covers at least 90% of the current year's liability or 100% of last year's, whichever is smaller.
The result also feeds relocation math. Moving from a no-income-tax state like Florida to Illinois means budgeting for a new 4.95% stream, while moving out means adjusting withholding in the other direction. Either way, keep the estimate inside a budget calculator so the state line item sits next to housing and savings instead of being discovered at filing time.
Homeowners can flip the credit math during a house hunt: a $6,000 annual property tax bill generates a $300 credit, but the underlying tax still costs $5,700 net, so factor the full bill into the true cost of ownership alongside mortgage interest and insurance. Re-run the numbers each year, since exemption values and county assessments both change.