Illinois Alimony Calculator 2026
Work out maintenance under the Illinois rule in 750 ILCS 5/504(b-1) from both incomes and the length of the marriage. The result is the statutory starting point; a judge decides the actual order. Everything runs privately in your browser, with no sign-up.
Not legal advice — a court decides. Illinois judges order the guideline amount below unless they find it inappropriate, and only after first deciding that maintenance is appropriate at all.
Illinois Alimony Formula & Factors
Illinois has a statutory maintenance formula. Under 750 ILCS 5/504, once a judge decides that maintenance is appropriate, guideline maintenance is 33⅓% of the payor's net annual income minus 25% of the recipient's net annual income. The result is then limited: the recipient's own net income plus maintenance may not exceed 40% of the couple's combined net income.
The guideline applies when the couple's combined gross income is under $500,000 a year and the payor has no child support or maintenance obligation from an earlier relationship. Above that ceiling, or when the judge finds the guideline inappropriate, maintenance is set from the factors in section 504(a) instead. If guideline maintenance plus child support would take more than 50% of the payor's net income, the court may also depart from the guideline.
Net income has the meaning given in section 505 of the same Act (the child support section), so it is a defined figure rather than simple take-home pay. Use the net income from the financial affidavits in the case if you have them.
What the Illustrative Estimate Is
When the Illinois rule does not cover your figures (combined gross income is $500,000 a year or more), this page shows an illustration instead and says so in the result. The illustration uses the reference method recommended by a commission of the American Academy of Matrimonial Lawyers (AAML) in 2007: 30% of the payor's gross income minus 20% of the recipient's gross income, limited so that the recipient ends up with no more than 40% of the couple's combined gross income. The method is set out in Mary Kay Kisthardt's article in the Journal of the American Academy of Matrimonial Lawyers (vol. 21, 2008) and summarised by Maryland's highest court in Boemio v. Boemio (2010).
The AAML method is not Illinois law and Illinois courts are not bound by it. It lists its own reasons to depart from the result, such as a spouse caring for a young or disabled child, age or health, or a career given up for the other spouse. It was written when alimony was still tax-deductible for the payer, and it does not apply when combined gross income is above $1,000,000 a year. Treat the figure as a starting point for a conversation with a lawyer, not as a prediction.
Illinois Alimony Rules at a Glance
| Point | Illinois rule | Source |
|---|---|---|
| Amount | 33⅓% of payor net income − 25% of recipient net income | 750 ILCS 5/504(b-1)(1)(A) |
| Limit | Recipient's net income + maintenance ≤ 40% of combined net income | 750 ILCS 5/504(b-1)(1)(A) |
| When the guideline applies | Combined gross income under $500,000 a year; payor has no prior support obligation | 750 ILCS 5/504(b-1)(1) |
| Length, marriage under 20 years | Years married × 0.20 (under 5 years) rising to × 0.80 (19 years) | 750 ILCS 5/504(b-1)(1)(B) |
| Length, 20 years or more | Equal to the length of the marriage, or indefinite | 750 ILCS 5/504(b-1)(1)(B) |
| Who decides | A judge, on the evidence in the case | 750 ILCS 5/504(b-1) |
| Federal income tax | Not deductible by the payer and not income to the recipient for agreements executed after 2018 | IRS Topic No. 452 |
Worked Example: Illinois Alimony Calculator
Take a payor with a net income of $6,000 a month and a recipient with $2,400 (gross incomes of $8,000 and $3,000, so $132,000 a year combined, under the $500,000 ceiling). One third of $6,000 is $2,000, and 25% of $2,400 is $600, a difference of $1,400. The limit is 40% of the combined net income of $8,400, which is $3,360, less the recipient's own $2,400: $960. Guideline maintenance is the lower figure, $960 a month ($11,520 a year).
For a 12-year marriage the factor is 0.52, so the guideline length is 12 × 0.52 = 6.24 years, or about 6 years 3 months.
These are the figures the calculator shows when the page first loads. A real order depends on evidence a calculator cannot see.
Illinois Alimony Duration Rules
The same section sets the guideline length. The length of the marriage when the divorce was filed is multiplied by a factor that rises with each year: 0.20 for under 5 years, 0.24 at 5 years, then 0.04 more for each further year up to 0.80 for 19 years. For a marriage of 20 years or more the court orders maintenance for a period equal to the length of the marriage or for an indefinite term.
Time for which temporary maintenance was paid during the case may be credited against that period, at the judge's discretion.
Is Alimony Taxable in Illinois?
For federal income tax, alimony or separate maintenance paid under a divorce or separation agreement executed after 2018 is not deductible by the payer and is not included in the recipient's income. Payments under an agreement executed before 2019 are generally still deductible by the payer and taxable to the recipient, unless the agreement was later modified and the modification expressly adopts the new rule (IRS Topic No. 452). Child support is never deductible and is not income.
This page does not cover Illinois state income tax. State rules are set separately and can differ from the federal rule, so check with the state tax agency or a tax adviser.
Modifying Illinois Alimony
Whether an order can be changed depends on its wording and on the type of support. In most cases either spouse can ask the court to modify periodic payments after a substantial change in circumstances, unless the decree or the spouses' agreement makes the support non-modifiable.
Read the order itself and 750 ILCS 5/504(b-1) before relying on a general rule, and get advice from a family lawyer licensed in Illinois about your own case. Nothing on this page is legal advice.
Last updated: October 2026. Sources: 750 ILCS 5/504 (Illinois General Assembly); AAML Commission recommendations (Kisthardt, 21 J. Am. Acad. Matrim. Law. 61); IRS Topic No. 452.
Frequently Asked Questions
How is alimony calculated in Illinois?
Illinois uses a statutory guideline in 750 ILCS 5/504(b-1): 33⅓% of the payor's net income minus 25% of the recipient's net income, limited so the recipient's net income plus maintenance is no more than 40% of the couple's combined net income. It applies when combined gross income is under $500,000 a year and the payor has no prior support obligation. A judge must first find that maintenance is appropriate and may depart from the guideline with written reasons.
Does Illinois use a formula for alimony?
Yes. Illinois is one of the few states with a maintenance formula written into statute, 750 ILCS 5/504(b-1)(1). It covers both the amount and the length of maintenance. Outside the guideline (combined gross income of $500,000 or more, a prior support obligation, or a finding that the guideline is inappropriate) the court decides from the factors in section 504(a).
How long does Illinois alimony last?
The guideline multiplies the years of marriage at filing by a factor: 0.20 for under 5 years, 0.24 at 5 years and 0.04 more for each additional year, up to 0.80 at 19 years. A 12-year marriage gives 12 × 0.52 = 6.24 years. For a marriage of 20 years or more the court orders maintenance for the length of the marriage or for an indefinite term.
Can Illinois alimony be modified?
It depends on the order. In most cases either spouse can ask the court to modify periodic payments after a substantial change in circumstances, unless the decree or the spouses' agreement makes the support non-modifiable. Check the wording of your order and 750 ILCS 5/504(b-1) before relying on a general rule.
Is alimony taxable in Illinois?
For federal income tax, alimony paid under a divorce or separation agreement executed after 2018 is not deductible by the payer and is not income to the recipient (IRS Topic No. 452). Agreements executed before 2019 generally keep the old treatment, deductible by the payer and taxable to the recipient, unless a later modification expressly adopts the new rule. This page does not cover Illinois state income tax, which is set separately.