Illinois Estate
Tax Calculator

Illinois imposes a state estate tax with an exemption of **$4 million**, one of the lower thresholds among estate-tax states. The tax is structured as a graduated rate that effectively ranges from approximately 0.8% to 16% on the taxable estate.

Illinois taxes the entire estate once it exceeds the $4 million threshold, not just the excess — this creates a "cliff" effect where an estate worth $4,000,001 owes tax on the full amount above zero.

This cliff effect is one of the most aggressive features in any state estate tax system. This means estate reduction strategies near the $4 million threshold can produce outsized savings.

Charitable gifts, lifetime transfers, and irrevocable trusts are frequently employed to keep Illinois taxable estates below the exemption.

The gap between the Illinois exemption (**$4 million**) and the federal exemption ($15 million) is substantial. Many Illinois estates that owe state estate tax owe nothing at the federal level.

Illinois does not offer portability of its estate tax exemption, so married couples often need separate planning to use both state exemptions.

Because Illinois taxes the entire estate once the exemption is exceeded (rather than just the excess), effective planning requires precise valuation. Obtain qualified appraisals for real estate, closely held business interests, and other hard-to-value assets to keep the estate below — or, if it must exceed — optimally above the threshold.

Credit shelter trusts (also called bypass trusts) are a cornerstone of Illinois estate planning for married couples. By funding a trust at the first spouse's death up to the Illinois exemption amount, both spouses' exemptions are preserved.

Without this structure, the first spouse's Illinois exemption is lost because no portability exists.

Illinois also imposes a generation-skipping transfer tax that mirrors the federal GST tax. Those structuring dynasty trusts or other multi-generational vehicles for Illinois estates must account for both the federal and state GST layers.

Cook County estates may also face higher administrative costs due to the volume of cases in the Cook County Circuit Court probate division.

Model the Illinois cliff effect and compare state versus federal estate tax liability using this estimator. The tool handles Illinois-specific rate calculations automatically.

Free for all states.

Illinois residents with taxable estates face a two-layer system: the federal estate tax (exemption of $15 million in 2025, top rate of 40%) and the Illinois estate tax (exemption of $4 million). The gap between these exemptions creates a range where only the state tax applies.

An estate valued at $8 million, for example, may owe Illinois estate tax while owing nothing at the federal level.

The federal return (Form 706) allows a deduction for state estate taxes paid, which partially offsets the double-taxation effect but does not eliminate it. The state tax is deductible on the federal return as an estate administration expense or under the state death tax credit rules, depending on the estate's circumstances.

The net result is that combined effective rates in Illinois can exceed 45% on estates large enough to trigger both layers.

Planning for this interaction requires modeling both taxes simultaneously. Strategies that reduce the Illinois taxable estate — such as lifetime gifts, charitable bequests, and irrevocable trusts — may also reduce federal exposure, but the relative benefit depends on where the estate falls within each jurisdiction's rate brackets.

Use our Illinois estate tax calculator to model both layers side by side, and check the Illinois probate cost calculator to estimate administration expenses.

Federal law permits a surviving spouse to use the deceased spouse's unused exclusion (DSUE) — commonly called portability — by timely filing Form 706 for the first-to-die spouse. This allows married couples to shelter up to $30 million federally without trust-based planning.

However, most estate-tax states, including Illinois, do not offer portability of the state exemption.

This asymmetry makes bypass trusts (also called credit shelter trusts or B trusts) essential in Illinois. At the first spouse's death, funding a bypass trust up to the Illinois exemption amount preserves that exemption for state tax purposes.

Without the trust, the unlimited marital deduction passes everything to the surviving spouse tax-free at the first death — but the surviving spouse's estate then has only one Illinois exemption, effectively wasting the first spouse's.

The bypass trust should be sized carefully. Overfunding it beyond the Illinois exemption wastes the marital deduction benefit; underfunding it fails to capture the full state exemption.

For married couples with estates above $4 million but below $15 million, the bypass trust is the single most impactful planning tool available. Review your plan with the Illinois estate tax estimator, and use the executor fee calculator to account for administration costs in your projections.

The $4 million Illinois exemption establishes a lower threshold than the federal exemption, making proactive estate reduction strategies more urgent. Irrevocable trusts are the primary vehicle: irrevocable life insurance trusts (ILITs) remove life insurance proceeds from the taxable estate, spousal lifetime access trusts (SLATs) allow married couples to remove assets while retaining indirect access, and qualified personal residence trusts (QPRTs) transfer a home at a discounted gift tax value.

Annual exclusion gifting — currently $19,000 per recipient (2025) — reduces the taxable estate dollar-for-dollar without consuming the lifetime gift exemption. For Illinois residents near the $4 million threshold, a sustained gifting program over several years can bring the estate below the state exemption entirely.

Charitable remainder trusts (CRTs) and charitable lead trusts (CLTs) offer additional reduction while generating income tax deductions.

GRATs (grantor retained annuity trusts) are particularly effective in low-interest-rate environments, transferring asset appreciation to beneficiaries with minimal or zero gift tax cost. For Illinois business owners, entity-level planning — family limited partnerships, LLCs with valuation discounts, and buy-sell agreements — can reduce the reportable value of closely held interests for both state and federal purposes.

Compare strategies using the Illinois estate tax calculator or find a Illinois estate planning attorney.