How Illinois decides how long alimony lasts
Most states leave the duration of alimony to judicial discretion. Illinois does not. Where the maintenance guideline applies, 750 ILCS 5/504(b-1)(1)(B) sets the length with a formula:
Length of the marriage × a statutory multiplier = the period maintenance is paid. The multiplier rises with each additional year of marriage, from 0.20 for the shortest marriages to 0.80 at nineteen years.
Two details matter more than people expect:
- Duration and amount are decided separately. The amount calculation uses income information, while the guideline-duration estimate begins with the length of the marriage.
- The marriage is measured to the date the case was filed, not to the date you separated and not to the date the judgment is entered. Couples who separate years before anyone files often find the clock kept running the whole time, which can move them into a higher band or over the twenty year line entirely.
The Illinois alimony duration table
This is the complete table from 750 ILCS 5/504(b-1)(1)(B). The right-hand column works the multiplier through for a marriage at the start of each band, which is the calculation the tool above performs.
| Length of marriage | Multiplier | Example |
|---|---|---|
| Less than 5 years | 0.20 | 4 years → 0.8 years |
| 5 to 6 years | 0.24 | 5 years → 1.2 years |
| 6 to 7 years | 0.28 | 6 years → 1.7 years |
| 7 to 8 years | 0.32 | 7 years → 2.2 years |
| 8 to 9 years | 0.36 | 8 years → 2.9 years |
| 9 to 10 years | 0.40 | 9 years → 3.6 years |
| 10 to 11 years | 0.44 | 10 years → 4.4 years |
| 11 to 12 years | 0.48 | 11 years → 5.3 years |
| 12 to 13 years | 0.52 | 12 years → 6.2 years |
| 13 to 14 years | 0.56 | 13 years → 7.3 years |
| 14 to 15 years | 0.60 | 14 years → 8.4 years |
| 15 to 16 years | 0.64 | 15 years → 9.6 years |
| 16 to 17 years | 0.68 | 16 years → 10.9 years |
| 17 to 18 years | 0.72 | 17 years → 12.2 years |
| 18 to 19 years | 0.76 | 18 years → 13.7 years |
| 19 to 20 years | 0.80 | 19 years → 15.2 years |
| 20 years or more | None | Length of the marriage, or indefinite |
The multiplier applies to the actual length of the marriage, not to the bottom of the band. A marriage of 12 years and 8 months still uses 0.52, so the period is about 6.6 years rather than 6.2.
The twenty year line
Every other step in the table adds four percentage points. The step at twenty years is not a step at all. It removes the formula.
For a marriage of 20 years or more, the statute directs the court, in its discretion, to order maintenance either for a period equal to the length of the marriage or for an indefinite term. There is no multiplier, and no arithmetic ceiling.
The practical gap is enormous. A marriage that ends one month short of twenty years produces roughly 15.9 years of maintenance under the 0.80 multiplier. The same marriage one month later can produce twenty years, or no end date whatsoever. Nothing else in Illinois maintenance law turns on a single month in the way this does.
If your marriage is close to the twenty year mark, the filing date is a strategic decision and not an administrative one. It is worth a conversation before anything is filed, whichever side of the payment you expect to be on.
Fixed-term, reviewable and indefinite alimony
The number of years is only half the answer. What kind of award you have determines whether that number is genuinely the end. Under 750 ILCS 5/504(b-4.5) there are three forms:
- Fixed-term. The court sets an end date, and when the term expires maintenance is barred. It cannot be revived later. If your circumstances change after the term ends, there is nothing left to modify.
- Reviewable. The court sets a term and states that the award is reviewable. At the end of it the parties come back and the court decides whether maintenance should be extended, modified, or ended, making the findings the statute requires. This is common where the recipient is retraining or returning to work and nobody can yet say how that will go.
- Indefinite. The court sets no termination date. Maintenance continues until it is modified or terminated under 750 ILCS 5/510. This is the form available after a marriage of twenty years or more.
"Indefinite" is not the same as "permanent", and the difference is worth being clear about. It means no end date has been set, not that the obligation is untouchable. It remains open to modification on a substantial change in circumstances, which is why retirement, serious illness and involuntary job loss are litigated as often as they are.
When alimony ends early
Three events end the obligation to pay future maintenance under 750 ILCS 5/510, and they apply whether or not your judgment mentions them:
- 01The death of either party.
- 02The remarriage of the person receiving maintenance. This operates by law on the date of the new marriage. A payor who keeps paying after that date can generally seek reimbursement.
- 03Cohabitation by the recipient with another person on a resident, continuing conjugal basis.
The third is the one that produces litigation. It does not mean a roommate and it does not mean dating. Courts look at whether the relationship functions like a marriage: how long it has run, how much time the couple spend together, whether finances are intermingled, whether holidays and family life are shared. The burden sits on the paying spouse to prove it, and when it began matters as much as whether it happened.
Separately from these three, maintenance can be modified or terminated on a substantial change in circumstances. A genuine, good faith retirement, a serious health event, or an involuntary loss of income can all support a modification. Deliberately reducing your own income to escape an obligation generally does not: courts can and do calculate maintenance on what a spouse is capable of earning.
Credit for temporary maintenance already paid
Many people pay maintenance for a year or more while the divorce is pending, under a temporary order made during the case. The statute allows that time to count. Any term of temporary maintenance paid under a court order may be applied as a corresponding credit against the duration of the final award, as the court determines.
It is discretionary rather than automatic, which is exactly why it needs to be raised. On a long-running case, this can be a year or two off the back end of the obligation.
How much will it be?
Duration comes from the length of the marriage. The monthly figure comes from somewhere else entirely: 33⅓% of the payor's net income minus 25% of the payee's net income, limited so the recipient does not end up with more than 40% of the couple's combined net income.
That cap governs more cases than the formula does. For a full explanation with worked examples, use the Illinois spousal support calculator, which answers the how much question the same way this page answers how long.
Illinois alimony duration: common questions
How long does alimony last in Illinois?
For guideline cases, the length of the marriage multiplied by a statutory factor between 0.20 and 0.80, rising with the length of the marriage. A ten year marriage produces about 4.4 years. After twenty years, the court may order maintenance for the length of the marriage or indefinitely.
Is there permanent alimony in Illinois?
Illinois uses the word indefinite rather than permanent, and it is available after a marriage of twenty years or more. It means no end date is set, not that the award can never change. It stays open to modification and it still ends on death, remarriage or qualifying cohabitation.
Does alimony stop automatically if my ex remarries?
Yes. The obligation to pay future maintenance terminates by operation of law on the date of the remarriage, whether or not your judgment says so.
What if my ex moves in with a new partner?
Maintenance terminates if the recipient cohabits with another person on a resident, continuing conjugal basis, but not automatically. The paying spouse has to bring it to court and prove the relationship is marriage-like rather than casual, and establishing when it began is part of the case.
Can alimony be extended past its end date?
It depends entirely on which type you have. Reviewable maintenance can be extended at the review. Fixed-term maintenance is barred once the term expires, and no later change in circumstances brings it back. Check which one your judgment gave you, because the difference is permanent.
Is the marriage measured from separation or from filing?
From the date the divorce action was commenced. Time spent separated but still married counts toward the total, which is why long informal separations can push a couple into a higher band or past the twenty year line.
Does a higher income mean a longer term?
No. Income sets the amount, not the duration. Two couples married the same length of time get the same guideline period no matter how differently they earn.
How accurate is this calculator?
The duration arithmetic follows the statute exactly, and for a guideline case it is the number a court would start from. What it cannot tell you is whether the guideline applies to your case at all, whether the award will be fixed-term, reviewable or indefinite, or whether temporary maintenance you have already paid should shorten it. Those decisions change the outcome more than the multiplier does.
Discuss the duration estimate
The tool calculates a guideline duration from the marriage length entered. It cannot determine whether the guideline applies, classify an award as fixed-term, reviewable, or indefinite, interpret an existing judgment, or decide whether temporary payments affect the final term. For help reviewing those questions, visit the Rockford spousal-support and alimony service page or contact Vernsten Law.
Related: Illinois spousal support calculator · Illinois child support calculator · Spousal support in Illinois · Divorce law · Family law
This page explains the Illinois maintenance guideline in general terms and is not legal advice. Reading it does not create an attorney-client relationship. The duration ordered in your case depends on your particular facts and on the discretion of the judge.