Illinois Spousal Maintenance Calculator

An eight-year marriage, for example, produces 8 × 0.36, or about 2.9 years of maintenance. For marriages of twenty years or longer, the court orders maintenance either for a period equal to the length of the marriage or for an indefinite term. Indefinite does not mean forever; it means there is no built-in end date, and the award stays in place until it is modified or terminated under the rules below.

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What “net income” means

The formula runs on net income as the statute defines it, which is not take-home pay. Net income is gross income from all sources minus federal and state income tax, Social Security and Medicare tax, and a short list of other statutory deductions. Contributions to a 401(k), health insurance premiums, union dues, and the like are not subtracted for this purpose, so net income under the statute is usually higher than what lands in a bank account.

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Gross income is also broader than a salary. Bonuses, commissions, overtime, self-employment income, rental income, and investment income all count, and a court can impute income to a spouse who is voluntarily unemployed or underemployed. For a business owner, the starting point is the business’s actual earnings, not what the owner chose to pay themselves.

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Tax can be calculated two ways: a standardized amount based on the tax tables, or an individualized amount that reflects the person’s actual filing status and deductions. The two methods can produce different net figures, and which one applies is often argued. Because a change of a few thousand dollars in either spouse’s net income moves the maintenance number, getting the income figures right is where most of the work in a maintenance case happens.

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Since 2019, maintenance has not been deductible to the payor or taxable to the recipient for federal purposes, and Illinois follows the federal treatment. The formula’s percentages were revised at the same time to account for that change, which is why older calculators and older advice give different numbers. Child support is calculated after maintenance, using the adjusted incomes; see the Illinois child support calculator.

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When maintenance ends or changes

Maintenance ends automatically when either spouse dies, when the receiving spouse remarries, or when the receiving spouse lives with someone else on a resident, continuing conjugal basis (750 ILCS 5/510(c)). The last one is the most litigated. It is not a roommate or a dating relationship; courts look at whether the new relationship functions like a marriage, weighing the length of the relationship, the amount of time the couple spends together, the nature of their activities, whether they share finances and property, and whether they spend holidays and vacations together. In re Marriage of Herrin, 262 Ill. App. 3d 573 (4th Dist. 1994). The paying spouse has to go back to court to prove it; the obligation does not stop on its own.

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Whether an award can be modified before it ends depends on how it was structured. Fixed-term maintenance is available in marriages of less than ten years; it ends on a set date and cannot be extended. Reviewable maintenance runs for a set period and then comes back before the court, which decides whether to continue it, change it, or end it, and the recipient is expected to make reasonable efforts toward self-support in the meantime. Indefinite maintenance, typical after long marriages, has no end date but can be modified or terminated on a substantial change in circumstances.

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Any modifiable award can be changed when one spouse shows a substantial change in circumstances (750 ILCS 5/510(a-5)): a real, involuntary drop in the payor’s income, a significant rise in the recipient’s, or the payor’s retirement at a normal retirement age, among others. A voluntary pay cut or a career change taken to reduce support does not count. The court looks at the same factors it used to set maintenance in the first place, plus the efforts each spouse has made since. Post-judgment changes are handled through a post-decree modification.

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The parties can also agree that maintenance is non-modifiable, in amount, duration, or both. That certainty cuts both ways, and it is a decision to make deliberately at the time of settlement rather than discover later.

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Common mistakes that throw the number off

Using gross income. The 33⅓ percent and 25 percent figures apply to net income. Running the formula on gross overstates the payment, sometimes by a third.

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Skipping the 40 percent cap. The receiving spouse’s net income plus maintenance cannot exceed 40 percent of the couple’s combined net income. At most income gaps the cap, not the percentages, sets the number, and a calculator that ignores it is wrong more often than right.

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Measuring the marriage to the wrong date. Duration is based on the length of the marriage from the wedding to the date the divorce petition was filed, not to the judgment. The multiplier steps up at each anniversary, so the filing date can add or remove years.

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Running the formula when it does not apply. Above $500,000 in combined gross income, or where the payor already supports a prior family, the formula does not control and the judge sets maintenance on the statutory factors.

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Assuming a tax deduction. For divorces finalized after 2018, maintenance is not deductible to the payor and not taxable income to the recipient. Older calculators and older advice still assume the reverse.

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Questions about this calculator

Is this an alimony calculator? Yes. Illinois calls it maintenance; other states and most people call it alimony or spousal support. Same thing.

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Is this the official Illinois maintenance calculator? There is no official state calculator. The formula is in 750 ILCS 5/504(b-1), and this page applies it as written, including the 40 percent cap and the duration table. What a court orders depends first on whether maintenance is appropriate at all.

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Does the calculator work for temporary maintenance while the case is pending? The same formula is the usual starting point for temporary maintenance, but courts have more latitude with temporary awards, and the parties’ actual expenses during the case matter more.

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What if we agree to a different number? Spouses can agree to more, less, none, or a lump sum, and courts approve those agreements unless they are unconscionable. Knowing the guideline figure is what lets you judge whether a proposed number is fair.

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Does maintenance stop if my ex moves in with someone? It can, if the relationship is a resident, continuing conjugal one, meaning it functions like a marriage. The paying spouse has to bring a petition and prove it; payments do not stop automatically. Courts look at the length of the relationship, shared finances, whether they live together full time, and how the couple presents themselves.

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Can maintenance be modified if the payor retires? Yes, if the retirement is at a reasonable age and made in good faith. Retirement is one of the recognized grounds for a substantial change in circumstances. Early retirement taken to avoid paying support is treated differently.

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What is the difference between fixed-term, reviewable, and indefinite maintenance? Fixed-term ends on a set date and cannot be extended; it is available when the marriage lasted less than ten years. Reviewable comes back before the judge at the end of the period. Indefinite has no end date but can be modified on a substantial change in circumstances.

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Can a prenuptial agreement waive maintenance? Yes. Illinois enforces maintenance waivers in a valid premarital agreement unless enforcing the waiver would leave a spouse eligible for public assistance, in which case the court can order enough to avoid that.

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Does the length of the marriage count separation? Yes. Duration is measured from the date of the marriage to the date the petition was filed, not the date the spouses separated and not the date the judgment is entered.

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