Alimony · IL
Illinois alimony and spousal support calculator
Illinois turns two net incomes and the length of the marriage into a guideline amount and a guideline term, once a judge finds maintenance appropriate.
Rules read on official Illinois pages on · Checked by Radif Partners · How we calculate
- Income counted
- Net income
- $8,000 vs $3,000 a month
- $1,400
- a month under the rule
- 12-year marriage
- 74.88 months
- Rules read on
- October 8, 2026
Illinois guideline maintenance is one-third of the payor's net income minus 25% of the payee's net income, and the payee's net income plus maintenance may not exceed 40% of the couple's combined net income (750 ILCS 5/504(b-1)(1)(A)). The guideline applies only when combined gross income is under $500,000 a year and the payor owes no support from a prior relationship. With $9,000 and $2,400 of monthly net income, it gives $2,160 a month. Duration is the length of the marriage at filing times a factor that starts at 0.2 below 5 years and rises to 0.8 just under 20; an 11-year marriage gives 5.28 years. From 20 years on, the judge orders maintenance for as long as the marriage lasted or for an indefinite term. The court must first decide that maintenance is appropriate under the § 504(a) factors.
Estimated spousal support in Illinois, per month
$1,400
Duration: up to 75 months
| One-third of the payor’s net income | $2,667 |
| Minus 25% of the payee’s net income | $1,917 |
| 40% limit (40% of combined net − payee net) | $1,400 |
| Guideline monthly maintenance | $1,400 |
| Duration factor | 12 years × 0.52 |
The guideline applies only if the spouses' combined gross income is under $500,000 a year and the payor owes no support from a prior relationship; otherwise the court sets the amount from the § 504(a) factors.
The 40% limit applies: the payee's net income plus maintenance may not exceed 40% of the combined net income.
Estimate under the Illinois formula as published; eligibility, the judge's findings and an agreement between spouses decide the real order. How this is calculated.
Two steps, and the first can end the case
Section 504(b-1) begins with a bar: unless the court finds an award appropriate, maintenance is denied whatever the length of the marriage. Only after that finding does the arithmetic start. That order matters in practice, because a payee who cannot show need under the § 504(a) factors gets nothing, even if the guideline would produce a large figure. When the judge departs from the guideline, § 504(b-2) requires findings that state what the guideline would have given and why it was not followed.
Where the 40% limit bites
The formula subtracts a quarter of the payee's net income from a third of the payor's. A second test then caps the result so that the payee ends up with no more than 40% of what both spouses net together. When the incomes are far apart, the first test decides: $9,000 against $2,400 a month yields $2,160. When they are closer, the ceiling takes over. At $9,000 and $4,500, the raw formula would give $1,875, but the cap brings it to $900. Both incomes are net, and maintenance paid in the pending case is left out of both.
| Years married | Factor |
|---|---|
| 0 to under 5 | 0.20 |
| 7 to under 8 | 0.32 |
| 10 to under 11 | 0.44 |
| 13 to under 14 | 0.56 |
| 16 to under 17 | 0.68 |
| 19 to under 20 | 0.80 |
From a fraction of the marriage to its full length
The term is the marriage length at the time the action was filed multiplied by the factor for that length. Eleven years gives 63.4 months. At 20 years the fraction disappears: a 23-year marriage leads either to 276 months, the full length, or to indefinite maintenance, at the judge's choice. Temporary maintenance paid while the case was pending may be credited against the term (§ 504(b-1)(1.5)). The order must say whether maintenance is fixed-term, indefinite, reviewable or reserved.
Two more checks sit beside the formula. If guideline maintenance and child support together exceed 50% of the payor's net income, the court may set non-guideline amounts. And orders entered before 2019 that stay tax-deductible are modified with a gross-income version of the formula, not this one.
The Illinois rule this calculator applies
Scope. Post-dissolution maintenance under 750 ILCS 5/504(b-1); guideline applies only if the court first finds maintenance appropriate. Temporary maintenance (§ 501) may be credited against the guideline duration (§ 504(b-1)(1.5)).
Amount. 750 ILCS 5/504(b-1)(1)(A): if the parties' combined gross annual income is less than $500,000 and the payor has no child support or maintenance obligation from a prior relationship, guideline maintenance = 33 1/3% of the payor's net annual income minus 25% of the payee's net annual income, but maintenance plus the payee's net income may not exceed 40% of the parties' combined net income. If guideline maintenance plus child support exceeds 50% of the payor's net income, the court may set non-guideline amounts. (A-1): modifications of pre-2019 tax-deductible orders use 30% of payor gross minus 20% of payee gross, capped at 40% of combined gross.
Duration. 750 ILCS 5/504(b-1)(1)(B): duration = length of the marriage at the time the action was commenced x the factor for that length (0.20 for < 5 years, rising by 0.04 per full year to 0.80 for 19 to < 20 years). For a marriage of 20 years or more, the court in its discretion orders maintenance for a period equal to the length of the marriage or for an indefinite term.
Eligibility. 750 ILCS 5/504(a) factors decide whether maintenance is appropriate; under (b-1) the court bars maintenance unless it finds an award appropriate, and only then applies the guideline (or non-guideline maintenance after considering the (a) factors, with findings under (b-2)).
Worth knowing in Illinois
- Unpaid maintenance accrues simple interest and each missed installment is a judgment that creates a lien on the obligor's property by operation of law (750 ILCS 5/504(b-5), (b-7)). source
- The court must state whether maintenance is fixed-term, indefinite, reviewable or reserved (750 ILCS 5/504(b-2)(3)). source
- Maintenance paid in the pending case is excluded from both gross and net income for the guideline (750 ILCS 5/504(b-3), (b-3.5)). source