Updated October 2, 2026. Quick answer: Illinois charges no estate tax on an estate of $4,000,000 or less with no taxable gifts. Above that, the tax is the lower of two results, each worked out with the tax itself deducted from its base: the Attorney General’s credit-table result, or 40% of the amount over $4,000,000. A $5,000,000 estate owes $285,714 (computed) and a $6,000,000 estate owes $456,071 (computed here, and equal to what the Attorney General’s own calculator printed for the same amounts on October 2, 2026). Enter your two amounts below.
Calculate your Illinois estate tax
The first box is the Attorney General’s field, Illinois Tentative Taxable Estate. The second is Illinois Tentative Taxable Estate Plus Adjusted Taxable Gifts, which must be at least as large as the first. Leave the second blank and this page uses the first amount, which is the right entry when there are no adjusted taxable gifts. The Attorney General’s own page requires both boxes.
The result is the Illinois estate tax only. It runs on this page and sends nothing anywhere. The Attorney General lists Form 700, a 2023 to 2026 decedents instruction sheet and Form 4350a, which it describes as a computation worksheet, on its estate tax page.
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Answer againHow the Attorney General’s calculator reaches the number
The Attorney General publishes a calculator for decedents from 2013 on, and its script is public. Its two boxes carry the labels used above. This page follows the script’s steps:
- Take the first amount and subtract the tax from the previous trial (zero on the first trial).
- Subtract $60,000 and look the result up in the credit table below: the tax on the first dollar of the bracket plus the bracket’s rate times the amount above its floor.
- Repeat with the new tax until the result moves by less than $1. The tax is deductible from its own base, which is why it takes several trials.
- Federal limit test: if 40% of the second amount, less the tax, less $4,000,000, is smaller than that tax, replace the tax with that figure and iterate the same way until it moves by $1 or less.
- Round to the dollar.
The statute that sets the credit points back to the federal estate tax as it stood before 2002: the State tax credit is “the full credit calculable under Section 2011 or 2604 of the Internal Revenue Code as the credit would have been computed and allowed under the Internal Revenue Code as in effect on December 31, 2001”. The script is how the Attorney General turns that into a number.
Solving the federal-limit step by itself gives a closed form, computed here from the script’s constants: the tax equals 0.4 divided by 1.4 of the amount over $4,000,000, which is 28.571%. Where that limit is the lower test it is the whole answer, so the tax rises from zero in step with the excess: $28,571 (computed) at $4,100,000 and $142,857 (computed) at $4,500,000.
A worked example: a $5,000,000 estate
Entering 5000000 in both boxes runs seven credit-table trials, computed here from the script’s table:
| Trial | Tax carried in | Estate less that tax | Less $60,000, looked up | Tax from the table |
|---|---|---|---|---|
| 1 | $0 (computed) | $5,000,000 (computed) | $4,940,000 (computed) | $391,600 (computed) |
| 2 | $391,600 (computed) | $4,608,400 (computed) | $4,548,400 (computed) | $347,741 (computed) |
| 3 | $347,741 (computed) | $4,652,259 (computed) | $4,592,259 (computed) | $352,653 (computed) |
| 4 | $352,653 (computed) | $4,647,347 (computed) | $4,587,347 (computed) | $352,103 (computed) |
| 5 | $352,103 (computed) | $4,647,897 (computed) | $4,587,897 (computed) | $352,164 (computed) |
| 6 | $352,164 (computed) | $4,647,836 (computed) | $4,587,836 (computed) | $352,158 (computed) |
| 7 | $352,158 (computed) | $4,647,842 (computed) | $4,587,842 (computed) | $352,158 (computed) |
The credit-table result settles at $352,158. The federal limit test then gives 40% of ($5,000,000 less $352,158 less $4,000,000), or $259,137. That is lower, so the limit applies, and iterating it gives $285,714 (computed). The Attorney General’s calculator, driven in a browser on October 2, 2026, printed the same final figure.
The credit table in the Attorney General’s script
These are the 21 brackets in the script, read from its source file (sha256 in the kit’s data). The right-hand column is the rate on the amount above each bracket’s floor.
| Amount looked up is at least | but less than | Tax on the first dollar of the bracket | Rate on the amount above the bracket’s floor |
|---|---|---|---|
| $0 | $40,000 | $0 | 0.0% |
| $40,000 | $90,000 | $0 | 0.8% |
| $90,000 | $140,000 | $400 | 1.6% |
| $140,000 | $240,000 | $1,200 | 2.4% |
| $240,000 | $440,000 | $3,600 | 3.2% |
| $440,000 | $640,000 | $10,000 | 4.0% |
| $640,000 | $840,000 | $18,000 | 4.8% |
| $840,000 | $1,040,000 | $27,600 | 5.6% |
| $1,040,000 | $1,540,000 | $38,800 | 6.4% |
| $1,540,000 | $2,040,000 | $70,800 | 7.2% |
| $2,040,000 | $2,540,000 | $106,800 | 8.0% |
| $2,540,000 | $3,040,000 | $146,800 | 8.8% |
| $3,040,000 | $3,540,000 | $190,800 | 9.6% |
| $3,540,000 | $4,040,000 | $238,800 | 10.4% |
| $4,040,000 | $5,040,000 | $290,800 | 11.2% |
| $5,040,000 | $6,040,000 | $402,800 | 12.0% |
| $6,040,000 | $7,040,000 | $522,800 | 12.8% |
| $7,040,000 | $8,040,000 | $650,800 | 13.6% |
| $8,040,000 | $9,040,000 | $786,800 | 14.4% |
| $9,040,000 | $10,040,000 | $930,800 | 15.2% |
| $10,040,000 | no upper limit | $1,082,800 | 16.0% |
Illinois estate tax on larger estates
Each row runs the same steps as the calculator above, with the second amount equal to the first.
| Illinois tentative taxable estate | Illinois estate tax | Which test sets it | Tax as a share of the amount over $4,000,000 |
|---|---|---|---|
| $4,100,000 | $28,571 (computed) | federal limit | 28.6% (computed) |
| $4,500,000 | $142,857 (computed) | federal limit | 28.6% (computed) |
| $5,000,000 | $285,714 (computed) | federal limit | 28.6% (computed) |
| $6,000,000 | $456,071 (computed) | credit table | 22.8% (computed) |
| $8,000,000 | $680,634 (computed) | credit table | 17.0% (computed) |
| $10,000,000 | $926,923 (computed) | credit table | 15.4% (computed) |
| $12,000,000 | $1,195,517 (computed) | credit table | 14.9% (computed) |
| $15,000,000 | $1,609,310 (computed) | credit table | 14.6% (computed) |
| $20,000,000 | $2,298,965 (computed) | credit table | 14.4% (computed) |
Every figure in the second column matched the result the Attorney General’s calculator page printed for the same amount when it was driven in a browser on October 2, 2026. The federal limit is the lower test up to $5,359,167 and the credit table is the lower test from $5,359,168 up (computed by running every estate in between): at $6,000,000 the credit table sets the tax at $456,071 (computed).
What the second box changes
In the federal limit test the second amount replaces the estate, so adjusted taxable gifts can create a tax on an estate that is under $4,000,000. The credit-table result uses only the first amount.
| First amount | Second amount, with gifts | Illinois estate tax | Which test sets it |
|---|---|---|---|
| $4,200,000 | $4,600,000 | $171,429 (computed) | federal limit |
| $3,900,000 | $5,000,000 | $244,565 (computed) | credit table |
| $2,000,000 | $6,000,000 | $92,910 (computed) | credit table |
| $4,800,000 | $5,500,000 | $332,014 (computed) | credit table |
| $6,000,000 | $7,000,000 | $456,071 (computed) | credit table |
A first amount of $3,900,000 with a second amount of $5,000,000 owes $244,565, although $3,900,000 alone owes nothing. Below the exclusion, with no gifts, the Attorney General’s calculator prints a negative number (a negative $285,714 (computed) for $3,000,000); a tax cannot be negative, so this page shows $0 and says what the script printed.
What the Illinois statute says
The Attorney General says “By Illinois law, The Illinois Attorney General administers the Illinois Estate Tax.” “Estate taxes must be filed with the Office of the Attorney General.” Payment goes elsewhere: “Any and all payments of Illinois estate tax, interest and penalties must be paid directly to the Illinois State Treasurer.”
The act imposes the tax on property with an Illinois connection: “An Illinois estate tax is imposed on every taxable transfer involving transferred property having a tax situs within the State of Illinois.” The exclusion amount is set in the definition of the State tax credit, which recognizes “the exclusion amount of only (i) $2,000,000 for persons dying prior to January 1, 2012, (ii) $3,500,000 for persons dying on or after January 1, 2012 and prior to January 1, 2013, and (iii) $4,000,000 for persons dying on or after January 1, 2013”. The calculator on this page is for the last of those, deaths on or after January 1, 2013.
The return follows the federal calendar: “The Illinois transfer tax shall be paid and the Illinois transfer tax return shall be filed on the due date or dates, respectively, including extensions, for paying the federal transfer tax and filing the related federal return.” The federal side is on the federal estate tax exemption page.
Where this calculator stops
Property outside Illinois. The statute reduces the tax for it: “the amount of the Illinois estate tax shall be the state tax credit, as defined in Section 2 of this Act, reduced by the amount determined by multiplying the state tax credit with respect to the taxable transfer by the percentage which the gross value of the transferred property not having a tax situs in Illinois bears to the gross value of the total transferred property.” The Attorney General’s calculator has only the two boxes above and neither asks where the property is, so neither applies that reduction. If part of the estate is outside Illinois, a preparer has to work that part out.
A separate Illinois QTIP election. The act allows one: “The person required to file the Illinois return may elect on a timely filed Illinois return a marital deduction for qualified terminable interest property under Section 2056(b)(7) of the Internal Revenue Code for purposes of the Illinois estate tax that is separate and independent of any qualified terminable interest property election for federal estate tax purposes.” Whatever it does to the tentative taxable estate has to be done before the number goes into the first box.
Other states. This is Illinois only. Rates and exclusions for the other states with an estate tax are on the estate tax by state page, and the Illinois rules in prose are on the Illinois estate tax page.
Common mistakes
- Entering the gross estate in the first box. The Attorney General’s field is the tentative taxable estate, and its Form 4350a is listed as the computation worksheet.
- Expecting the whole estate to be taxed once it passes $4,000,000. The tax starts at zero and rises with the excess: $28,571 (computed) at $4,100,000, not a tax on the whole estate.
- Putting a second amount smaller than the first. The second box adds gifts, so it can only be equal or larger.
- Treating the result as a filing. The return is Form 700, filed with the Attorney General, and the payment goes to the State Treasurer.
Related: Illinois estate tax, estate tax by state, the lifetime gift and estate tax exemption, who pays the estate tax, and Illinois probate cost.
Sources
- Illinois Estate and Generation-Skipping Transfer Tax Act, 35 ILCS 405 (Illinois General Assembly): https://www.ilga.gov/Legislation/ILCS/Articles?ActID=609&ChapterID=8
- Illinois Attorney General, Filing Estate Taxes in Illinois: https://illinoisattorneygeneral.gov/estate-taxes/
- Illinois Attorney General, 2013-2026 Decedents Estate Tax Calculator: https://illinoisattorneygeneral.gov/estate-taxes/2013-2025-estate-calculator
- Illinois Attorney General, estate tax calculator script (CalcHtm.js): https://illinoisattorneygeneral.gov/application/estate-tax-calculator/CalcHtm.js
Read from the Illinois Attorney General’s pages and the Illinois Compiled Statutes linked above on October 2, 2026. General information, not legal or tax advice. Your own facts decide the outcome, and an estate attorney, a preparer or the Attorney General’s estate tax section is the right place to confirm anything consequential.