How is Alimony Calculated in Illinois?

If you're going through a divorce in Illinois and wondering about alimony — called "maintenance" in Illinois law — you're in one of the relatively few states where real math exists. Illinois has a statutory formula for the amount and a statutory multiplier for the duration. Both are tied directly to income and marriage length, which means you can produce a concrete estimate before setting foot in a courtroom.

That said, the formula is not absolute. Courts can deviate based on a set of statutory factors, and for high-income couples (combined gross income over $500,000) the formula doesn't apply at all. Understanding when the formula governs and when discretion takes over is the key to reading your own situation accurately.

The Illinois Maintenance Formula

Under 750 ILCS 5/504(b-1), Illinois courts apply a specific formula when combined gross income is under $500,000 and no prior maintenance obligations exist from a previous marriage. The formula uses each spouse's net monthly income — after taxes — not gross income.

The 40% combined income cap prevents situations where maintenance plus the payee's own income would exceed 40% of what both spouses earn together — a built-in ceiling that keeps the formula from producing results that would over-compensate the receiving spouse.

The Marriage-Length Duration Multiplier

Illinois ties maintenance duration directly to marriage length using a statutory multiplier table under 750 ILCS 5/504(b-1)(1)(B). Unlike states that leave duration entirely to judicial discretion, Illinois gives both sides a precise calculation to work from.

The duration percentage starts at 20% for marriages under 5 years and increases by 4% for each additional year of marriage, capping at 80% for a 19-year marriage. For marriages of 20 years or more, courts may award maintenance for an indefinite period — though even indefinite awards remain subject to modification if circumstances change.

The Four Types of Maintenance in Illinois

Illinois courts may structure maintenance in four ways depending on the circumstances of the case.

Fixed-term maintenance is the most common outcome when the formula applies. A specific end date is set based on the duration multiplier. When that date arrives, maintenance ends — no additional court action required unless modification was sought before termination.

Indefinite maintenance is available for marriages of 20 years or more, or in shorter marriages where self-sufficiency is genuinely unlikely due to age, disability, or severe career disruption. No fixed end date is established, but the award remains subject to modification.

Reviewable maintenance allows the court to set a review date — at which point both parties return to court and the judge reassesses whether maintenance should continue, and in what amount. This is used when the future financial picture is uncertain at the time of divorce.

Reserved maintenance means the court does not award maintenance now but preserves the right to do so later if circumstances change. This is uncommon and requires the court to make specific findings about why a current award would be inappropriate.

When Courts Deviate from the Formula

The formula produces a guideline, not a mandate. Courts may deviate — awarding more, less, or for a different duration — when the guideline result would be unjust or inappropriate given the specific circumstances. Any deviation requires written findings.

The statutory factors courts consider for deviation include: the income and property of each spouse; the realistic needs of each spouse; the present and future earning capacity of each spouse; any impairment of earning capacity due to domestic duties; the standard of living established during the marriage; the duration of the marriage; tax consequences; contributions and services provided by the spouse seeking maintenance; valid agreements between the parties; and any other equitable factors the court deems relevant.

The 2025 Incarceration Law Change

Remarriage, Cohabitation, and Termination

Remarriage of the receiving spouse automatically terminates maintenance in Illinois. No court order is needed — the obligation ends by operation of law.

Cohabitation on a resident, continuing conjugal basis also terminates maintenance under 750 ILCS 5/510(c). Illinois is specific about what qualifies: occasional overnight stays do not constitute cohabitation; the relationship must be continuous and conjugal in nature. The paying spouse bears the burden of demonstrating that qualifying cohabitation is occurring.

Either party's death terminates maintenance unless the divorce agreement or decree expressly provides for continuation — which is rare and must be explicitly negotiated.

Modification is available under 750 ILCS 5/510 when there has been a substantial change in circumstances — significant income change, serious illness, job loss, or the paying spouse's retirement. The formula is reapplied to the new income figures when a modification is sought, and the court may also adjust the duration.

Tax Treatment: What Changed in 2018

For divorces finalized on or after January 1, 2019, maintenance payments are no longer deductible for the paying spouse and no longer taxable income for the receiving spouse — federally and for Illinois state income tax. This is a permanent change under the Tax Cuts and Jobs Act of 2017.

The tax change directly affects negotiations. Under the old rules, a payer could absorb a higher gross payment because the deduction offset the after-tax cost. Under the current rules, every dollar of maintenance comes directly out of after-tax income — which is why both sides account for this when finalizing amounts.

Putting It Together: A Worked Example