In Illinois there is no such thing as a separate "alimony" law. Spousal support, spousal maintenance and alimony are three names for the same thing, and one statute governs all of it: 750 ILCS 5/504. The calculator below applies the guideline formula in subsection (b-1)(1)(A) to work out how much would be paid each month.
Enter three figures and you will see your estimated range in seconds. Everything behind the number is explained below the calculator: the formula, the 40% cap that quietly decides most cases, and the situations where the guideline does not apply at all.
Marriage length sets how long maintenance may last. 20+ years can be indefinite.
Attorney Eric Vernsten, a former prosecutor, reviews every estimate personally. No obligation.
This tool provides a general estimate based on the Illinois maintenance guidelines (750 ILCS 5/504) and the information you enter. It is not legal advice and does not create an attorney-client relationship. Guideline maintenance generally applies when the parties' combined gross income is under $500,000; above that, or in other circumstances, a court has broad discretion. Speak with attorney Eric Vernsten for guidance specific to your situation.
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Since 2015 Illinois has used a guideline formula rather than leaving the figure entirely to the judge. Where the guideline applies, 750 ILCS 5/504(b-1)(1)(A) sets the amount in one line:
33⅓% of the payor's net income, minus 25% of the payee's net income. The result, added to what the payee already earns, may not leave the payee with more than 40% of the parties' combined net income.
The statute is written in annual figures. This calculator works in monthly figures because that is how people think about a support payment, and because the formula is a straight percentage, the two give the same answer.
Notice what is not in the formula. Not fault. Not who filed. Not who wanted the divorce. Illinois removed fault from maintenance a long time ago, and no amount of bad behavior by a spouse changes the guideline number.
Most articles mention the cap as a footnote. In practice it is doing the work far more often than the headline formula is, and understanding why tells you more about your own case than the percentages do.
Work through the algebra and a clean threshold falls out. The 33⅓/25 formula only produces the lower of the two numbers when the higher earner's net income is more than about 5.25 times the lower earner's. Below that ratio, the 40% cap is the smaller figure, and the cap is what you will actually be ordered to pay.
That is a large share of real divorces. Two working spouses, one earning meaningfully more than the other but not five times more, is an ordinary Illinois case, and in every one of them the guideline formula is effectively a ceiling that never gets reached.
One spouse nets $7,000 a month, the other nets $1,000. That is a 7:1 ratio, comfortably past the threshold.
Now one spouse nets $7,000 and the other nets $3,000. A 2.3:1 ratio, which is a much more typical gap.
Anyone who read the formula and stopped there would have budgeted for $1,583 and been wrong by nearly $600 a month.
One spouse nets $5,000, the other nets $4,500. The formula still produces a positive number, about $542. The cap does not: 40% of $9,500 is $3,800, which is already less than the $4,500 the payee earns without any support. The guideline result is zero.
When two spouses earn similar amounts, the guideline generally produces nothing, no matter how long the marriage lasted.
This is the input people get wrong most often. Illinois does not mean the number at the bottom of your payslip after health insurance, retirement contributions and everything else your employer takes out.
Under 750 ILCS 5/504, net income carries the meaning given in Section 505, the child support statute, with maintenance in the pending case excluded. In practice that means gross income from all sources, reduced by either the standardized tax amount published by the state, or your individualized tax amount where the court uses your actual tax figures, and then by the adjustments the statute allows.
Two consequences worth knowing:
The calculator asks for net monthly income. If you enter gross pay, your estimate will come out far too high.
The formula is not universal. Two conditions have to be met before a court uses it at all:
Fail either test and the case becomes a non-guideline maintenance case. The court then decides the amount and the duration by weighing the fourteen factors in 750 ILCS 5/504(a), which include the property and income of each spouse, realistic present and future earning capacity, any impairment of earning capacity caused by devoting time to domestic duties, the standard of living established during the marriage, the length of the marriage, the age and health of both parties, contributions one spouse made to the other's education or career, tax consequences, and any valid agreement between the parties.
A non-guideline case is not a free-for-all. The court has to state its reasoning, and if it departs from the guideline it must say what the guideline figure would have been and why it is not ordering that. But the outcome is genuinely open in a way a guideline case is not, and it is the point at which the quality of your advocacy starts to matter a great deal.
High-income cases are the common example. Above $500,000 combined gross, a percentage of income can produce a figure far beyond anything either spouse actually spent during the marriage, so Illinois lets the court look at real need and real standard of living instead.
Amount and duration are decided by two separate parts of the same statute, and they have nothing to do with each other. The amount comes from the incomes. The duration comes almost entirely from one number: how long you were married, multiplied by a fixed statutory factor under 750 ILCS 5/504(b-1)(1)(B).
A short marriage between two high earners can produce a large payment for well under a year. A twenty-year marriage between two modest earners can produce a small payment with no end date at all.
Because that question has its own answer, it has its own tool: the Illinois alimony duration calculator shows the number of years in full, free, with no form to fill in first.
For any divorce finalized after December 31, 2018, no. The federal Tax Cuts and Jobs Act removed the payor's deduction and stopped treating maintenance as taxable income to the recipient. The payor pays with after-tax dollars and the recipient receives it tax free. That is precisely why the Illinois formula was rewritten to run on net income: the old version used gross figures because the tax burden used to move with the payment.
Orders entered before January 1, 2019 can keep the old treatment. Where such an order is modified after that date, it retains the same federal tax treatment unless both parties expressly agree otherwise, and the statute applies a different formula to it: 30% of the payor's gross income minus 20% of the payee's gross, capped so the payee does not exceed 40% of combined gross.
If you are modifying an older Illinois order, do not use the calculator above. The figures are calculated on a different basis and you need advice specific to your decree.
Where the guideline applies, it is 33⅓% of the payor's net income minus 25% of the payee's net income, limited so the payee's own income plus maintenance does not exceed 40% of the couple's combined net income. The lower of those two results is the guideline amount.
Net, for the formula itself. Gross, for the $500,000 threshold that decides whether the formula applies at all. Mixing those two up is the single most common error in online estimates.
Almost certainly, unless the higher earner nets more than roughly 5.25 times the lower earner. Below that ratio the cap produces the smaller number, and the smaller number is the one the court orders.
Yes, but the gap between the two incomes is what drives the result. Where the incomes are close, the guideline typically produces nothing, because the cap is already satisfied by what the lower earner brings in.
The guideline stops applying and the case is decided on the fourteen statutory factors instead. Outcomes vary widely, and this is the category where experienced representation changes the number the most.
No. Illinois is a no-fault state for these purposes, and marital misconduct is not one of the factors the court weighs when setting maintenance.
Yes. Spouses can settle on an amount and a term by agreement, and a valid agreement between the parties is itself one of the statutory factors. Courts routinely approve sensible negotiated maintenance, which is usually faster and considerably cheaper than litigating it.
The arithmetic follows the statute exactly. What it cannot know is whether your reported income is the income a court would attribute to you, whether the guideline applies to your case at all, or how a judge would weigh the fourteen factors if it does not. Treat the range as a starting point for a conversation, not as your answer.
Attorney Eric Vernsten has handled Illinois family law matters in Rockford for over a decade, including maintenance disputes where the reported income and the real income were not the same number. Run your figures through the calculator above and he will review them personally and call you with a precise estimate, including whether the guideline applies to your case at all. There is no obligation, and the call usually takes ten minutes.
Related: How long alimony lasts in Illinois · 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. What a court orders in your case depends on your particular facts and on the discretion of the judge.
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