How Illinois calculates maintenance
Illinois calls spousal support "maintenance," and it stands apart from most states because the legislature actually wrote a calculation formula into law. Under 750 ILCS 5/504(b-1), when the couple's combined gross income is under $500,000 and the paying spouse has no prior support obligations to another party, maintenance is calculated as 33.33% of the payor's net annual income minus 25% of the payee's net annual income. The statute then applies a cap: the maintenance award, when added to the payee's own net income, cannot push the payee's total income above 40% of the couple's combined net income. If the formula output would cross that line, the award is reduced so the payee's total lands at exactly 40% of combined net income. This combination of a percentage formula and an income-share cap makes Illinois one of the more predictable states for a rough maintenance estimate, at least for couples under the $500,000 combined-income threshold.
Duration is calculated with similar precision. 750 ILCS 5/504(b-1)(1)(B) multiplies the number of years married by a statutory factor: 0.20 for marriages under five years, rising in roughly 0.04 increments per additional year of marriage — 0.24 for five-to-under-six years, 0.28 for six-to-under-seven years, and so on up through 0.80 for marriages of 19 to just under 20 years. A ten-year marriage, for example, uses a 0.44 multiplier, which works out to about 4.4 years (roughly 52.8 months) of maintenance. Once a marriage reaches 20 years, the statute hands the decision to the judge: the court may order maintenance for a term equal to the full length of the marriage, or it may order indefinite (permanent) maintenance, entirely at its discretion. There is no cap-off point built into the statute for long marriages beyond that discretionary choice.
When the formula doesn't apply — because combined gross income is $500,000 or more, or because the payor already owes support to someone else — Illinois courts fall back to the discretionary factors listed in 750 ILCS 5/504(a). Those factors cover each party's income and property, needs, earning capacity, any impairment of earning capacity from time spent on domestic duties, the time and expense needed to gain further education or training, the marital standard of living, duration of the marriage, age and health of the parties, tax consequences, contributions to the other spouse's education or career, any valid prenuptial or postnuptial agreement, and a general catch-all for any other factor the court finds just and equitable. Unlike the formula path, there is no fixed percentage or cap in this fallback scenario — the judge weighs the full list case by case.
Illinois places no minimum marriage-length requirement on eligibility itself; a short marriage can still produce a maintenance award, it's simply that the duration multiplier scales the term down for shorter marriages. The $500,000 combined-income ceiling is the only hard gate that determines whether the formula applies at all, rather than a marriage-length threshold like some other states use.
On fault, Illinois is unambiguous: it is a no-fault divorce state, and marital misconduct — including adultery — is not one of the enumerated 750 ILCS 5/504(a) factors that a court considers in setting maintenance. Whatever led to the divorce, the maintenance analysis in Illinois stays focused on income, earning capacity, marriage length, and the couple's financial circumstances rather than who was "at fault." This is a meaningful contrast with states like Georgia, where an adultery-caused separation can bar alimony outright.
No major overhaul of Illinois maintenance law has been identified for the 2023–2026 period. The 33.33%/25% formula, the 40% combined-income cap, and the duration multiplier table all date back to Illinois's 2015 maintenance guideline reforms and remain the current law for divorces proceeding in 2026. If your case involves multiple income streams, a prior support obligation, or income near the $500,000 combined threshold, the formula math above should be treated as a starting point rather than the final word — those situations often push a case toward the discretionary factors instead.
Statute citation: 750 ILCS 5/504 (Illinois Compiled Statutes, Marriage and Dissolution of Marriage Act).
Frequently Asked Questions
Does Illinois have an actual alimony formula?
Yes. Illinois is one of the few states with a true statutory guideline formula. Under 750 ILCS 5/504(b-1), when combined gross income is under $500,000 and the payor has no prior support obligations, maintenance equals 33.33% of the payor's net annual income minus 25% of the payee's net annual income, capped so the payee's total income does not exceed 40% of the couple's combined net income.
How long does maintenance last in Illinois?
750 ILCS 5/504(b-1)(1)(B) applies a duration multiplier tied to years married, from 0.20 for marriages under 5 years up to 0.80 for marriages of 19 to just under 20 years, in roughly 0.04 increments per year. For marriages of 20 years or more, the court may order maintenance for a period equal to the length of the marriage or an indefinite term, at its discretion.
Does adultery affect alimony in Illinois?
No. Illinois is a no-fault divorce state, and marital misconduct is not listed among the factors in 750 ILCS 5/504(a) that courts weigh for maintenance amount or duration.
What happens if combined income is $500,000 or more?
The statutory formula in 750 ILCS 5/504(b-1) does not apply once combined gross income reaches $500,000, or if the payor already owes support from a prior relationship. In that case the court sets maintenance using the discretionary factors in 750 ILCS 5/504(a) instead of the formula.
Is this Illinois maintenance calculator legal advice?
No. It applies the published statutory formula and duration multiplier for planning purposes only. A judge retains discretion in many cases, and you should confirm your specific numbers with a licensed Illinois family-law attorney.