Illinois estate-tax estimates can change substantially as an estate grows. The examples below make those differences easier to compare, but they only work when the same assumptions apply to every figure.
The estate-size comparisons in the next section assume an Illinois resident, all property having Illinois tax situs, no adjusted taxable gifts, and an estate figure after allowable deductions and applicable Illinois adjustments but before deducting Illinois estate tax. These are planning estimates rounded to whole dollars.
Compare estates using the same assumptions
These amounts use the same calculation as our Illinois estate tax calculator:
- $4 million tentative taxable estate: $0 estimated Illinois estate tax.
- $4.1 million: approximately $28,571.
- $5 million: approximately $285,714.
- $6 million: approximately $456,071.
- $8 million: approximately $680,634.
- $10 million: approximately $926,923.
The state’s published fact sheet also shows $0 at $4 million and $285,714 at $5 million. Other figures above are illustrations from this site’s estimator. Iteration and rounding can produce small differences from the official calculator.
Why a single percentage can mislead
Illinois uses an interrelated computation in which the state estate-tax deduction affects the amount being calculated. The statutory framework is in 35 ILCS 405/2.
The $4 million exclusion should not be treated as a simple subtraction followed by one universal rate. Nor should the percentage from one example be applied to every estate value.
For instance, the $5 million example produces a tax of about 5.71% of the entered estate. That percentage describes this example; it is not a general Illinois estate-tax rate.
Your net worth may not be the right input
The examples use a tentative taxable estate, which may differ from a household’s net worth or probate inventory. Start with what belongs in the estate, then identify allowable deductions.
A married couple also should not enter their combined assets and assume that the result describes the tax at either death. Asset ownership and transfers between spouses matter. Our guide to married-couple and QTIP planning explains why the two deaths need separate attention.
Prior taxable gifts can change the calculation. Property outside Illinois may require apportionment. Neither adjustment is included in the comparisons above.
Compare keeping assets with making a lifetime gift
A separate question is whether giving assets away changes the result. Start with the same $4.8 million tentative taxable estate and no earlier taxable gifts. Keeping the assets until death produces an estimated Illinois tax of $228,571. Making a completed $2.8 million taxable gift, leaving $2 million in the estate and $2.8 million in adjusted taxable gifts, produces an estimate of $92,910.
That is $135,661 less Illinois estate tax. This illustration assumes unchanged values and deductions, no growth or spending, all property having Illinois tax situs, and a gift excluded from the estate at death. It does not include the possible income-tax cost of a lost basis adjustment or federal gift or estate tax.
The Lifetime Gifting Explorer shows how the result changes across different gift amounts. The prior-gifts guide explains why a gift can still count in the calculation even when it reduces the eventual tax.
Turn an example into a useful planning question
Choose the example closest to your properly determined estate figure, then ask what makes your circumstances different: insurance, a family business, a spouse’s needs, old gifts, or property elsewhere.
Use the calculator to organize an estimate and print the result. A zero result is not a determination that no return is required, and none of these figures includes federal estate tax, interest, or penalties.
Bring your estimate and the underlying records to a planning consultation. The useful next step is to identify which facts and planning choices could change your family’s result.