Illinois Estimated Tax Payments
If your income does not come with withholding attached, Illinois expects you to pay as you go. This calculator works out whether you need to make estimated payments, how much each quarterly voucher should be, and which safe harbor protects you from a penalty.
Illinois Estimated Tax Payment Calculator
Illinois only requires them when you expect to owe more than $1,000 after withholding and credits.
- 90% of this year's tax$0
- 100% of last year's tax$0
- You need to cover $0
- Covered by withholding$0
- Still to pay this year$0
- Per quarterly voucher$0
Do you need to make estimated payments?
The United States runs a pay-as-you-go tax system. An employee satisfies it automatically through withholding; everyone else has to do it deliberately. Illinois requires estimated payments when you expect to owe more than $1,000 after withholding and credits — which usually means one of these applies to you:
- Self-employment, freelance or 1099 contract income
- Rental property income
- Substantial interest, dividends or capital gains
- Retirement income above the Illinois subtraction, or a Roth conversion
- A partnership or S-corporation share that does not carry pass-through withholding
- Unemployment compensation with no voluntary withholding elected
- A working spouse where the household's combined withholding falls short
Two exemptions exist: people aged 65 or over who live permanently in a nursing home, and farmers with at least two-thirds of federal gross income from farming. There is also no penalty if you were not required to file an Illinois return at all last year.
The four due dates
| Installment | Income period covered | Due | Share |
|---|---|---|---|
| Q1 | January 1 – March 31 | April 15, 2026 | 25% |
| Q2 | April 1 – May 31 | June 15, 2026 | 25% |
| Q3 | June 1 – August 31 | September 15, 2026 | 25% |
| Q4 | September 1 – December 31 | January 15, 2027 | 25% |
The periods are famously uneven. The second installment covers only two months, and the fourth covers four — so a business that earns most of its money over the summer is expected to have paid a quarter of the year's tax by mid-April, before much of that money has arrived. The annualized income method on Form IL-2210 exists precisely to fix that, at the cost of more paperwork.
The two safe harbors, and why Illinois is generous
You do not have to predict your income correctly. You only have to hit one of two targets, and you may use whichever is lower:
90% of this year's Illinois tax, or
100% of last year's Illinois tax
in four timely installments, and no underpayment penalty applies — even if you end up owing thousands in April.
The second option is where Illinois is notably kinder than the IRS. Federally, once your prior-year adjusted gross income passes $150,000 the safe harbor rises to 110% of the prior year. Illinois has no such rule. One hundred percent of last year's Illinois tax protects you at any income level, which makes the prior-year figure the obvious anchor for anyone whose income is climbing.
| Approach | Paid in installments | Due in April | Penalty? |
|---|---|---|---|
| 90% of this year | $8,100 | $900 | No |
| 100% of last year | $4,000 | $5,000 | No |
| Paid nothing | $0 | $9,000 | Yes — on all four installments |
The middle row is the interesting one. Paying $1,000 a quarter leaves a $5,000 bill in April, but no penalty at all — and the $5,000 sat in your own account earning interest for the year rather than the state's. That is a legitimate cash-flow advantage, provided you actually have the $5,000 when April arrives.
Working out the number
Illinois tax is simple enough to estimate on the back of an envelope: (expected income − subtractions − exemptions) × 4.95%, less any credits. On $80,000 of expected income with one exemption that is ($80,000 − $2,925) × 4.95% = $3,815, or $954 a quarter.
Two refinements are worth making. First, self-employment income is not the same as revenue — deduct your business expenses first, and remember the deductible half of federal self-employment tax reduces federal AGI and therefore the Illinois figure too. Second, if a spouse has a job, their withholding counts toward the household's total, so subtract it before dividing by four. The Illinois income tax calculator produces a full-year figure to feed into the calculator above.
For a self-employed Illinois resident with no other income, putting aside 25% to 32% of net profit covers federal self-employment tax, federal income tax and Illinois income tax together. Move it into a separate account the day each payment lands, not at quarter end — money that stays in the operating account has a way of not being there in April.
What an underpayment actually costs
Illinois computes the penalty installment by installment on Form IL-2210, comparing the required payment for each quarter with what was actually paid by that date. A shortfall attracts the late-payment penalty — 2% if cured within 30 days of the due date, 10% after that — plus interest at the federal underpayment rate, currently 7% a year and running through December 31, 2026.
Two things soften it. Withholding is treated as paid evenly across the year no matter when it was actually taken, so if you or your spouse has a job, increasing withholding late in the year can retroactively repair an early-year underpayment. And there is no penalty at all if the balance after withholding and credits is $1,000 or less, or if your prior-year liability was zero.
Paying
| Method | Cost | Notes |
|---|---|---|
| MyTax Illinois ACH debit | Free | Schedule payments in advance; gives a confirmation number |
| Credit or debit card | Processor fee | Through approved third-party processors |
| ACH credit / EFT | Bank fee | Register on Form EFT-1; suits businesses |
| Check with Form IL-1040-ES | Postage | Works, but leaves no timestamped proof |
Federal payments run in parallel on Form 1040-ES or through IRS Direct Pay, and they are typically the larger of the two. Doing both on the same day, four times a year, is the habit that keeps this manageable.
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People also ask about Illinois estimated taxes
Anyone who reasonably expects their Illinois tax to exceed $1,000 after withholding, pass-through payments and credits. In practice that means the self-employed, landlords, retirees with large investment income, people with substantial capital gains, and anyone whose wage withholding does not cover a second stream of income. Two groups are exempt: people aged 65 or over living permanently in a nursing home, and farmers with at least two-thirds of federal gross income from farming.
April 15, June 15, September 15 and January 15 of the following year — the same four dates as the federal payments, so you can write both checks at once. Illinois expects four equal installments of 25%. Note the uneven periods: the second installment covers only April and May, so income earned in the spring bunches up sooner than most people expect.
Pay the lesser of 90% of this year's tax or 100% of last year's tax, on time and in four installments, and no underpayment penalty applies however much you end up owing in April. Unlike the federal rules, Illinois has no 110% rule for higher incomes — 100% of the prior year is a complete shield at any income level. If last year's figure is the lower of the two, paying it in four equal parts is the simplest way to stay protected while your income grows.
A late-payment penalty applies to that installment — 2% if it is paid within 30 days of the due date and 10% after that — plus interest at the federal underpayment rate, which is 7% a year through the end of 2026. The penalty is computed on Form IL-2210, and the Department of Revenue normally works it out for you. Paying a missed installment late is always better than waiting until April, because the penalty stops accruing the day you pay.
Yes, and it is the easiest route. MyTax Illinois takes a free ACH debit from a checking or savings account and gives you a confirmation number. Credit and debit cards work through approved processors but carry a fee. Businesses can use ACH credit through Form EFT-1. The old method still works too: a check with the Form IL-1040-ES voucher, though you lose the timestamped proof of payment.
Two approaches. The safest is the prior-year safe harbor — pay 100% of last year's tax in four equal parts and stop worrying about this year's number entirely. The alternative is the annualized income method on Form IL-2210 Step 6, which lets you pay in proportion to when the income actually arrived. That suits seasonal businesses and anyone with a large one-off gain late in the year, but it takes more record-keeping.
Yes, and it is often the better option if you or a spouse has a job. Withholding is treated as paid evenly through the year regardless of when it was actually taken, so a large amount withheld in November can retroactively cure an underpayment from April. An estimated payment made in November cannot. Line 3 of Form IL-W-4 and Step 4(c) of the federal Form W-4 both let you add a flat amount per paycheck — the withholding guide covers both.
Almost certainly, and they are larger. The federal threshold is also $1,000, but federal tax on the same income is typically two to four times the Illinois figure, and the federal safe harbor rises to 110% of the prior year once your prior-year adjusted gross income passes $150,000. Federal payments go on Form 1040-ES or through IRS Direct Pay. The self-employment tax calculator works out both sides together.
Sources
- Illinois Department of Revenue — estimated payments
- IDOR — Form IL-1040-ES, estimated income tax payments
- IDOR — Form IL-2210 instructions, computing the underpayment penalty
- IDOR — current interest rates on underpayments
- IRS — estimated taxes
Estimates for planning. Penalty calculations depend on payment dates and on whether you elect the annualized income method, neither of which this tool models. Speak to a CPA or enrolled agent before setting your first year of estimated payments.