Illinois Estate Tax: The Basics 

Illinois is one of a small number of states that levies its own estate tax, and it applies to estates with a gross value exceeding $4 million. Unlike the federal estate tax — which only taxes the amount above the exemption threshold — Illinois calculates the tax on the full value of the estate from dollar one once that $4 million threshold is crossed. This is an important and often misunderstood distinction: a taxable estate of $4.1 million is not taxed only on the $100,000 above the exemption. The entire $4.1 million is subject to the tax calculation. 

Illinois estate tax brackets are published online and top out at 16% — but that figure is misleading without understanding how the calculation actually works. Because the tax applies to the full estate value from dollar one rather than only the amount above the exemption, an estate just over $4 million bears the full weight of those brackets on every dollar. When you calculate the resulting tax as a rate applied only to the amount over $4 million — the amount that actually pushed the estate into taxable territory — the effective marginal rate on that excess can reach as high as 28.5%. And counterintuitively, the effect is regressive: as the estate grows larger, that effective rate on the excess decreases, because the tax is being spread across a larger base. The proportional burden falls hardest on estates just over the $4 million threshold — making early planning especially critical in that range. 

For the most accurate, personalized estimate of Illinois estate tax liability, we direct clients to the Illinois Attorney General's official estate tax calculator, available at: 

https://illinoisattorneygeneral.gov/estate-taxes/2013-2025-estate-calculator. This tool, maintained by the state, provides a reliable projection based on your specific estate value. 

Planning Strategies: Credit Shelter Trusts and Disclaimer Trusts 

Two of the most effective tools for married couples seeking to reduce Illinois estate tax exposure are Credit Shelter Trusts (CSTs) and Disclaimer Trusts. Both strategies are designed to take full advantage of each spouse's $4 million Illinois exemption — but they accomplish this in different ways. 

Credit Shelter Trusts (also called Bypass Trusts or "B" Trusts) are established at the death of the first spouse. Assets up to the Illinois exemption amount ($4 million) are directed into the trust rather than passing outright to the surviving spouse. These trust assets benefit the surviving spouse during their lifetime — through income and discretionary principal distributions — but are not included in the survivor's taxable estate at their death. This preserves the first spouse's exemption and can effectively double the couple's combined exemption to $8 million. 

Disclaimer Trusts offer greater flexibility by allowing the surviving spouse to decide, after the first spouse's death, how much of the estate should flow into the trust. Rather than locking assets into a trust at the time of drafting, a disclaimer trust lets the survivor assess the estate's actual size, the tax environment, and their own financial needs before making an irrevocable disclaimer of assets into the trust. This approach is particularly useful when the size of the estate at death is uncertain, as it avoids over-funding or under-funding the bypass structure. 

The Critical Role of Proper Account Titling and Estate Plan Funding

Having a well-drafted trust is only half the equation. Funding the estate plan — meaning re-titling assets and updating beneficiary designations so that the right assets flow to the right entities — is equally essential. In fact, it is one of the most commonly overlooked steps in estate planning. 

If a married couple's assets are titled entirely in joint tenancy, or if beneficiary designations pass everything directly to the surviving spouse, those assets bypass the trust entirely. The result: the first spouse's Illinois exemption is lost. At the survivor's death, only one $4 million exemption is available — not two — and the estate may owe significantly more in state estate taxes than would have been the case with proper funding. 

Proper account titling is not a one-time exercise. It should be reviewed regularly — particularly after major life events such as a home purchase, an inheritance, a business sale, or any significant change in net worth or marital status. 

The Married Couple Advantage: Up to $8 Million in Combined Exemption

Unlike the federal estate tax, Illinois does not automatically offer portability — the ability for a surviving spouse to use the deceased spouse's unused exemption. This makes advance planning all the more critical for Illinois residents. However, when a Credit Shelter Trust or Disclaimer Trust is properly drafted and the estate plan is properly funded, a married couple can effectively shield up to $8 million from Illinois estate tax — $4 million per spouse. 

Achieving this outcome requires coordination between your estate planning attorney, your financial advisor, and often your CPA. It is not something that happens automatically by virtue of being married or having a will. The trust must be in place, the assets must be titled correctly, and the plan must be revisited as your estate grows and tax law evolves. 

A Hidden Layer of Complexity: IRAs and the Double Tax Problem 

The strategies discussed here represent only a portion of the planning landscape. Illinois estate planning — particularly for those with significant retirement assets — involves layers of complexity that require careful coordination across your financial advisor, CPA, and estate planning attorney. 

One of the most nuanced areas involves Individual Retirement Accounts (IRAs). Under the SECURE Act and its successor legislation, the rules governing inherited IRAs changed dramatically. For most non-spouse beneficiaries, inherited IRAs must now be fully distributed within 10 years — compressing what was once a decades-long tax deferral window into a much shorter timeframe and significantly accelerating ordinary income recognition for heirs. 

The question of whether to name a trust as the beneficiary of an IRA adds another layer of difficulty. While doing so can offer estate control and asset protection benefits, trusts named as IRA beneficiaries often trigger even faster distribution requirements. Where an individual non-spouse beneficiary has 10 years to draw down an inherited IRA, a trust that does not qualify as a "see-through" trust may be subject to a 5-year rule — requiring full distribution within just 5 years of the owner's death. This compresses taxable income into an even shorter window, often pushing distributions into the highest marginal tax brackets. Meanwhile, the IRA may already be subject to Illinois estate tax as part of the gross estate — creating a double taxation scenario where the same dollars are taxed once at the state estate level and again as ordinary income on the way out. 

There is, however, a frequently overlooked provision that can help offset this double tax burden: Income in Respect of a Decedent (IRD). When estate tax has been paid on an asset — such as an IRA — that will also generate taxable income when distributed, the tax code allows beneficiaries to claim a federal income tax deduction for the portion of estate tax attributable to that asset. In other words, if an IRA was included in a taxable estate and estate tax was paid on it, the beneficiary receiving distributions from that IRA may be able to deduct a proportionate share of the estate tax paid — meaningfully reducing the income tax owed on those distributions. Unfortunately, this deduction is vastly underutilized. Most beneficiaries are simply unaware it exists, and without a coordinated team of advisors flagging it at the right time, it is routinely missed — leaving real money on the table. 

Adding further complexity, the IRD deduction is based on federal estate tax paid — but many Illinois estates fall into a gap where Illinois estate tax is owed yet no federal estate tax is due, because the federal exemption ($13.61 million per individual as of 2024) is far higher than Illinois's $4 million threshold. In those cases, the IRD deduction offers little to no benefit, because there is no federal estate tax to reference. The Illinois estate tax paid in that margin between the two exemption levels effectively goes uncompensated — a silent cost that is almost never discussed and rarely planned for. 

Weighing the protective benefits of a trust beneficiary designation against this compounded tax burden is not a one-size-fits-all decision. It requires a thorough, coordinated analysis — one that accounts for the size and composition of the estate, the income tax brackets of the heirs, and the interaction between Illinois estate tax, federal income tax, and available deductions like IRD. 

Let's Talk 

These are exactly the kinds of interconnected planning challenges — spanning investment strategy, tax planning, and legal structure — where working with the right team makes a meaningful difference in outcomes. There are many more nuances beyond what is covered here, and no two situations are alike. Reach out to our team at Shoreline Financial Partners to learn more.