Illinois Estate Tax in 2026: Exemption, Rates & Calculator

How Illinois taxes an estate

Illinois computes two numbers and charges whichever is lower: (a) a calculation based on the frozen pre-2001 federal 'state death tax credit' table, and (b) 40% of the amount by which the taxable estate exceeds $4,000,000, each adjusted for the fact that the tax itself reduces the taxable amount. Because of that interaction, there's no single flat 'Illinois rate' to quote — the effective rate actually declines as the estate grows past a certain point, which is why this page doesn't show a simple bracket table.

Worked example

A $10,000,000 Illinois taxable estate owes $926,923 — reverse-engineered from and verified exactly against the Illinois Attorney General's own official estate tax calculator. At $5,000,000, by contrast, the tax is $285,714 (also matching the Attorney General's own published example) — a smaller estate, but a HIGHER effective rate on the amount above the exclusion, because the 40%-of-excess formula controls at that lower level while the credit-table formula controls at $10,000,000.

Rules worth knowing

• Illinois's own Attorney General's office — which administers this tax — describes the calculation as "interrelated" and points practitioners to its own online calculator rather than a printed worksheet, because it genuinely isn't a simple lookup.
• The $4,000,000 exclusion has not increased since 2013 and is not indexed for inflation, unlike the federal exemption.

Filing deadline

The federal Form 706 return, when required, is due 9 months after the date of death (IRC §6075(a)). Illinois's own Form 700 has its own deadline — confirm the exact requirement with the Illinois Attorney General's office (which administers Illinois estate tax, not the Department of Revenue) rather than relying on the federal date.

More on estate tax

For how federal estate tax works alongside state estate tax, the 2026 federal exemption, and spousal portability, see the full estate tax guide.