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Illinois Alimony Calculator (2026)

Illinois calls alimony maintenance and sets both the amount and the duration by statutory formula for most couples. Enter both net incomes and the length of the marriage to see the guideline amount, the 40% cap and how long payments are expected to last.

Figures reviewed 3 primary sources
Annual net incomes

Use income after taxes and mandatory deductions.

Marriage and eligibility

Estimated monthly maintenance

$1,333per month

Paid by the higher earner (payor) to the payee.

Per year
$16,000
Guideline duration
About 4.4 years

How we got there

33 1/3% of the payor's annual net income$33,333
25% of the payee's annual net income- $10,000
Formula amount$23,333
Cap: 40% of combined net income minus the payee's income$16,000
Guideline annual maintenance (lower of the two)$16,000
Duration factor for a 10-year marriage0.44
  • The 40% cap on the payee's share of combined net income limits the amount.
  • Net income follows the child support definition in section 505: gross income less federal and state taxes, Social Security and Medicare, and other mandatory deductions.
  • Marriage length is measured up to the date the divorce petition was filed.
Standing assumptions
  • Amount and duration formulas from 750 ILCS 5/504(b-1)(1) as amended effective January 1, 2019.
  • Maintenance is not deductible by the payor or taxable to the payee for orders entered after 2018.

Estimate only. Not legal advice.

Key 2026 numbers for Illinois

Amount formula
33 1/3% minus 25%
Of the payor's and payee's net incomes respectively.
Cap
40% of combined net
The payee's income plus maintenance may not exceed 40% of both incomes combined.
Duration factor
0.20 to 0.80
Multiplied by the length of the marriage; 20 years or more can be indefinite.
Applies below
$500,000
Combined gross income; above that the court uses the statutory factors.

When the guideline formula applies

Section 504 of the Illinois Marriage and Dissolution of Marriage Act first asks whether maintenance is appropriate at all, considering each party's income and property, needs, present and future earning capacity, contributions to the marriage, the standard of living, and the length of the marriage. If it is, and the parties' combined gross income is under $500,000 and the payor has no maintenance or child support obligation from a prior relationship, the court applies the guideline formula in section 504(b-1). Otherwise the court sets the amount and duration on the factors.

The amount

Guideline maintenance is 33 1/3% of the payor's net annual income minus 25% of the payee's net annual income. The result is capped so that the payee's net income plus maintenance does not exceed 40% of the parties' combined net income. Net income uses the child support definition in section 505: gross income less federal and state income taxes, Social Security and Medicare, and the other mandatory deductions, calculated either with the standardized tax tables or individualized figures.

Since January 1, 2019 the formula has run on net rather than gross income, because maintenance for orders entered after 2018 is no longer deductible by the payor or taxable to the payee under federal law.

How long it lasts

Duration is the length of the marriage, measured to the date the petition was filed, multiplied by a factor: 0.20 for marriages under 5 years, 0.24 for 5 years, then rising by 0.04 each year to 0.80 for 19 years. For marriages of 20 years or more, the court may order maintenance for a period equal to the length of the marriage or for an indefinite term. Courts can also designate maintenance as fixed-term, reviewable, or indefinite, and can extend or modify reviewable awards.

Deviations, termination and modification

A court that departs from the guidelines must state the guideline amount and duration and explain the reasons. Maintenance ends on the death of either party, the remarriage of the payee, or the payee's cohabitation with another person on a resident, continuing conjugal basis under section 510(c). A substantial change in circumstances, such as retirement or a large change in income, supports a petition to modify, and the parties can agree that maintenance is non-modifiable.

Worked example

  1. The payor's net income is $100,000 a year and the payee's is $40,000; the marriage lasted 10 years at filing.
  2. 33 1/3% of $100,000 is $33,333; 25% of $40,000 is $10,000; the formula gives $23,333.
  3. The cap is 40% of $140,000, or $56,000, minus the payee's $40,000, which is $16,000. The cap controls.
  4. The duration factor for a 10-year marriage is 0.44, so maintenance lasts about 4.4 years.

Guideline maintenance of $16,000 per year, about $1,333 per month, for roughly 4.4 years.

Illinois alimony questions

Is maintenance mandatory in Illinois?

No. The court first decides whether maintenance is appropriate under the section 504(a) factors. The formula sets the amount and duration only after that threshold finding.

Does the formula use gross or net income?

Net income since 2019, using the same definition as child support. The $500,000 eligibility threshold, by contrast, is measured on combined gross income.

Can maintenance be indefinite?

Yes, for marriages of 20 years or more the court may order it for the length of the marriage or indefinitely. Shorter marriages use the duration factors.

Does living with a new partner end maintenance?

Cohabitation on a resident, continuing conjugal basis terminates maintenance under section 510(c), retroactive to the date cohabitation began.

Sources

  1. 750 ILCS 5/504, maintenance
  2. 750 ILCS 5/510, modification and termination
  3. 750 ILCS 5/505, net income definition

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