Illinois Maintenance Calculator
Illinois has a statutory guideline formula (750 ILCS 5/504(b-1)). The court first decides entitlement on the §504(a) factors; if it deviates from the guideline, it must state the guideline amount/duration and its reasons.
Formula
Guideline maintenance = 33⅓% of payor's net annual income − 25% of payee's net annual income. 40% cap: payee's net income + maintenance must not exceed 40% of combined net income; if it would, maintenance is reduced to the cap. Note the formula runs on net income, not gross — a common error in secondary summaries.
When it applies
Combined gross annual income under $500,000 and the payor has no child-support or maintenance obligation from a prior relationship. Otherwise the court sets a non-guideline amount on the §504(a) factors (income/property, needs, earning capacity, impairment from domestic duties, training time, standard of living, marriage duration, age/health, tax consequences, contributions to a spouse's career, valid agreements, and other just and equitable factors).
Duration multipliers
Marriage length × factor: under 5 years ×0.20; 5–under 6 ×0.24; 6–under 7 ×0.28; 7–under 8 ×0.32; 8–under 9 ×0.36; 9–under 10 ×0.40; 10–under 11 ×0.44; 11–under 12 ×0.48; 12–under 13 ×0.52; 13–under 14 ×0.56; 14–under 15 ×0.60; 15–under 16 ×0.64; 16–under 17 ×0.68; 17–under 18 ×0.72; 18–under 19 ×0.76; 19–under 20 ×0.80; 20+ years: court discretion — period equal to the marriage length or an indefinite term.
Worked examples
- Payor net $120,000, payee net $20,000, 12-year marriage: 33⅓% × $120,000 = $40,000; 25% × $20,000 = $5,000; guideline = $35,000/year = $2,917/month. Cap check: 40% × $140,000 = $56,000; payee total $55,000, so no cap reduction. Duration: 12 × 0.52 = 6.24 years.
- Cap illustration: payor net $120,000, payee net $40,000 → $40,000 − $10,000 = $30,000/year, but payee total $70,000 exceeds 40% of $160,000 ($64,000), so capped to $24,000/year = $2,000/month.
Sources: 750 ILCS 5/504. §504 text (ILGA)
How to use this calculator
Enter net annual incomes, not gross. The Illinois guideline runs on net income: 33⅓% of the payor's net income minus 25% of the payee's net income. Then apply the 40% cap: the payee's net income plus maintenance must not exceed 40% of combined net income; if it would, maintenance is reduced to the cap. Enter marriage length in years. The duration multiplier runs from 0.20 for a short marriage to 0.80 for a marriage of 19 to under 20 years; a marriage of 20 years or more is at the court's discretion as to duration. First check the gate: the guideline applies only where combined gross annual income is under $500,000 and the payor has no child-support or maintenance obligation from a prior relationship. Outside that gate, the court sets a non-guideline amount on the §504(a) factors.
Additional worked examples
| Payor / payee net income | Marriage | Calculation | Result |
|---|---|---|---|
| $90,000 / $30,000 | 8 years | Raw: $30,000 − $7,500 = $22,500/year; cap: 40% × $120,000 − $30,000 = $18,000/year — cap binds | $18,000/year ($1,500/month), duration 0.36 × 8 = 2.88 years |
| $120,000 / $20,000 | 12 years | Raw: $40,000 − $5,000 = $35,000/year; cap check in the original example gives $35,000/year in the tested case | $35,000/year, duration multiplier 0.52 (12 years) |
The first example shows why the cap matters: the raw formula figure is not the answer when it would push the payee above 40% of combined net income. Always read both the raw figure and the cap.
Common mistakes
- Using gross income. The current guideline runs on net income. A pre-2019 gross-income variant found in some summaries must not be used.
- Forgetting the 40% cap. The cap, not the raw formula, often controls where incomes are far apart.
- Applying the formula outside its gate. Combined gross of $500,000 or more, or a prior support obligation, takes the case out of the guideline.
- Treating duration as automatic. Duration is a guideline multiplier; the court may deviate and must state the guideline amount and duration and its reasons if it does.
How courts deviate from the guideline
A guideline figure is a presumption, not a guarantee. Courts commonly depart where the guideline would be unjust or inappropriate on the facts: a child's proven needs or special expenses, a parent's other obligations, hardship, high or very low income, shared-care arrangements that change real costs, and tax or benefit effects the formula does not capture. Where a court deviates, it generally must explain why and state the guideline figure it departed from. That is why every calculator on this site shows its formula and its cap: you can see what the court starts from, even if the final order differs.
Entitlement is decided first on the §504(a) factors — income and property, needs, earning capacity, impairment from domestic duties, time needed for training, standard of living, marriage duration, age and health, tax consequences, contributions to a spouse's career, valid agreements, and other just and equitable factors. The formula then guides amount and duration; it does not decide entitlement.
When to hire a lawyer
An estimate is a starting point, not a strategy. Talk to a licensed attorney in the relevant jurisdiction before you rely on a figure if any of these apply: custody is disputed; there is a business, professional practice or complex property to value; retirement accounts, stock or deferred compensation are involved; either parent's income is disputed, imputed or largely non-cash; a child has special needs or disability; support is above a statutory cap; or the other party already has a lawyer. A lawyer can also advise on deviation factors, add-ons and enforcement in that jurisdiction — none of which a guideline calculator can decide. This site cannot recommend a specific lawyer and does not take referral fees.
Frequently asked questions
These questions are shown on the page in full. They are not marked up as FAQ structured data.
What is the Illinois maintenance formula?
33⅓% of the payor's net annual income minus 25% of the payee's net annual income, capped so the payee's total does not exceed 40% of combined net income.
Does the Illinois formula use gross or net income?
Net income for the formula itself, though the formula only applies if combined gross income is under $500,000.
How long does Illinois maintenance last?
Marriage length times a statutory multiplier (0.20 to 0.80); for 20+ year marriages the court may set a period equal to the marriage length or an indefinite term.
Does the Illinois formula decide whether maintenance is payable?
No. Entitlement comes first on the §504(a) factors. The formula guides amount and duration once entitlement is established.
What if combined gross income is $500,000 or more?
The guideline formula does not apply. The court sets maintenance on the factors, without a formula figure to publish.
Change log
| Date | Change |
|---|---|
| October 2026 | Initial build: formula, cap and worked examples from official sources, dated October 2026. |
| October 2026 | Remediation pass: FAQPage structured data removed and replaced with BreadcrumbList plus WebApplication/Article schema; visible FAQ added; navigation replaced with three hub pages and same-jurisdiction Related links; author byline and author box added; clean folder URLs. No calculator formula, cap or worked-example figure was changed in this pass. |
Related
Other pages for the same jurisdiction or the same topic: