The formula, and the ceiling that usually sets it.

The facts, in one place.

Six quotable sentences on the Illinois maintenance guideline.

1. The guideline applies when the parties' combined gross annual income is under $500,000 and the payor has no child support or maintenance obligation from a prior relationship; otherwise the court sets maintenance from the statutory factors (750 ILCS 5/504(b-1)(1)).
2. The amount is 33 1/3 percent of the payor's net annual income minus 25 percent of the payee's, and the payee's net income plus maintenance may not exceed 40% of the parties' combined net income (504(b-1)(1)(A)). Whenever the payee earns more than about a fifth of what the payor earns, the ceiling, not the formula, sets the amount.
3. Duration is the length of the marriage at filing times a factor: .20 under five years, rising four points a year to .80 at nineteen; at twenty years or more the court orders a term equal to the marriage or an indefinite one (504(b-1)(1)(B)).
4. Net income is the Section 505 figure: gross less the standardized tax amount (federal and state income tax for a single filer with the standard deduction and one exemption, plus FICA), read from the HFS conversion table, or an individualized tax amount when the court allows it (504(b-3.5); 505(a)(3)).
5. Example: a payor earning $150,000 and a payee earning $50,000, married 12 years. Net incomes of about $106,511 and $40,025; the formula gives $25,497 a year but the 40 percent ceiling cuts it to $18,589, or $1,549 a month, for 6 years and 3 months.
6. For an instrument executed after 2018, maintenance is neither deductible by the payor nor income to the payee, federally (Pub. L. 115-97 § 11051) and in Illinois, which starts from federal AGI; that is why the guideline was rewritten in 2019 on net rather than gross income.

Duration by length of the marriage.

The multiplier for each band, and what it yields at the band's first year.

How the guideline works.

Since the 2019 rewrite, Illinois sets maintenance by formula in the ordinary case: when the parties' combined gross income is under $500,000 and the payor carries no support obligation from a prior relationship, the amount is 33 1/3 percent of the payor's net income less 25 percent of the payee's, and the payee's net plus maintenance may not exceed 40 percent of combined net. The ceiling is not a corner case. It binds whenever the payee earns more than about a fifth of what the payor earns, so in most two-income households the ceiling, not the formula, is the number. Duration is the length of the marriage at commencement times a factor that climbs from .20 to .80 across the bands; at twenty years the court chooses between a term equal to the marriage and an indefinite one.

Net income is the Section 505 income-shares figure: gross less the standardized tax amount, which the Department of Healthcare and Family Services publishes as a gross-to-net table for a single filer with the standard deduction and one exemption, plus FICA; or an individualized amount where the statute allows it. This calculator approximates the standardized figure from the year's federal single brackets and standard deduction, the Illinois flat rate and exemption, and the FICA rates and wage base, all read from records on this site. It is close, not the table, and the court's figure governs. Because maintenance under an instrument executed after 2018 is neither deductible nor income, the transfer moves net income dollar for dollar, which is what the chart draws.

Methodology.

1. Inputs. Each spouse's gross annual income, the length of the marriage at filing in whole years, and whether the payor has a support obligation from a prior relationship.
2. The gate. Combined gross under $500,000 and no prior obligation (504(b-1)(1)); otherwise the tool reports that the court decides and computes nothing.
3. Net income. For each spouse, gross less: federal ordinary tax on gross minus the single standard deduction; Illinois tax at the flat rate on gross minus the personal exemption; Social Security tax to the wage base; Medicare tax; and the additional Medicare tax above $200,000. An approximation of the 505(a)(3)(C) standardized tax amount.
4. The amount. 33 1/3 percent of the payor's net less 25 percent of the payee's, then the lesser of that and 40 percent of combined net minus the payee's net (504(b-1)(1)(A)); never below zero.
5. The duration. The years of marriage times the band's factor from the record's table (504(b-1)(1)(B)); at 20 or more years, no figure, and the court's two choices are named.
6. After the transfer. Each spouse's net less or plus the annual amount, with no tax effect (Pub. L. 115-97 § 11051), and the payee's share of combined net, which equals exactly 40 percent when the ceiling binds.
7. Validation. The $150,000 / $50,000 / 12-year case pinned to the cent through both net incomes, the formula, the binding ceiling, and 6.24 years; a no-income payee where the formula governs; the $500,000 gate and the prior-obligation gate; a twenty-year marriage; and the FICA pieces at $250,000. A transcription error fails the build.
8. Not modeled. The HFS table itself (this is an approximation), child support in the same case and the 50 percent combined ceiling, the court's deviation and its findings, the (A-1) gross-income formula for modified pre-2019 orders, temporary maintenance credit, self-employment tax, itemized deductions, and any income that is not wages. Educational, not advice.

Sources.

1. 1. Illinois General Assembly, 750 ILCS 5/504(b-1) — Maintenance; amount and duration under the guidelines. That the guidelines apply when combined gross annual income is under $500,000 and the payor has no child support or maintenance obligation from a prior relationship (b-1)(1); the amount as 33 1/3 percent of the payor's net annual income minus 25 percent of the payee's, capped so the payee's net plus maintenance does not exceed 40 percent of combined net (b-1)(1)(A); the duration as the length of the marriage at commencement times the factor for its band, from .20 under five years to .80 at nineteen, and at twenty or more years a term equal to the marriage's length or indefinite in the court's discretion (b-1)(1)(B); the 50 percent combined-support ceiling in the preamble; and the gross-income formula for modified pre-2019 orders (A-1). Retrieved September 7, 2026; verified September 7, 2026.
2. 2. Illinois General Assembly, 750 ILCS 5/505(a)(3) — Net income; the standardized and individualized tax amounts. That net income is gross income minus either the standardized tax amount or the individualized tax amount (B); that the standardized tax amount is federal and state income tax for a single person claiming the standard deduction and one personal exemption, plus Social Security and Medicare tax at the FICA rate, with a conversion table promulgated by the Department of Healthcare and Family Services (C); and what the individualized amount aggregates (D). Section 504(b-3.5) adopts this definition for maintenance. Retrieved September 7, 2026; verified September 7, 2026.
3. 3. Illinois Department of Healthcare and Family Services, Income Shares — the standardized net income conversion table. The Department's gross-to-net conversion table that courts use for the standardized tax amount, which this tool approximates rather than reproduces. Retrieved September 7, 2026; verified September 7, 2026.
4. 4. Illinois General Assembly, 750 ILCS 5/510(c) — Termination of maintenance on death, remarriage, or cohabitation. That, unless the parties agree otherwise in writing, the obligation to pay future maintenance ends on the death of either party, the remarriage of the recipient, or the recipient's cohabitation on a resident, continuing conjugal basis, with reimbursement of payments made after that date. Retrieved September 7, 2026; verified September 7, 2026.
5. 5. U.S. Government Publishing Office, Pub. L. 115-97, § 11051 — Repeal of the deduction for alimony payments and the corresponding inclusion in income. That §§ 71 and 215 are repealed for any divorce or separation instrument executed after December 31, 2018, and for earlier instruments modified after that date when the modification expressly so provides: maintenance is neither deductible by the payor nor income to the payee. Retrieved September 7, 2026; verified September 7, 2026.
6. 6. Illinois General Assembly, 35 ILCS 5/203(a)(1) — Base income begins with federal adjusted gross income. That an individual's Illinois base income is federal adjusted gross income with the listed modifications, so maintenance excluded from federal income is excluded from Illinois income, and maintenance not deductible federally is not deductible in Illinois. Retrieved September 7, 2026; verified September 7, 2026.
7. 7. United States Code (Cornell LII), 26 U.S.C. § 3101 — Rate of tax on employees (Social Security and Medicare). The 6.2 percent old-age, survivors, and disability rate (a); the 1.45 percent hospital insurance rate (b)(1); and the additional 0.9 percent above $200,000 for an unmarried individual (b)(2). Retrieved September 7, 2026; verified September 7, 2026.
8. 8. Illinois General Assembly, 35 ILCS 5/201(b)(5.4) — Tax imposed; rate for individuals, trusts, and estates. The 4.95 percent rate on net income for taxable years beginning on or after July 1, 2017. Retrieved September 5, 2026; verified September 5, 2026.
9. 9. Illinois General Assembly, 35 ILCS 5/204 — Standard exemption; the additional exemption at 65 or for blindness. The basic exemption and its cost-of-living indexing rounded down to $25; the additional $1,000 for a taxpayer or spouse 65 or older, and again for blindness. Retrieved September 5, 2026; verified September 5, 2026.
10. 10. Internal Revenue Service, Rev. Proc. 2025-32 — 2026 inflation adjustments (tax rate tables § 4.01, capital gains § 4.03, AMT exemptions § 4.10). Every 2026 bracket boundary and base amount for individuals and for estates and trusts; the 0% and 15% capital-gain thresholds; the AMT exemption amounts. Retrieved September 4, 2026; verified September 4, 2026.
11. 11. Social Security Administration (Federal Register, 90 FR 49047), Cost-of-Living Increase and Other Determinations for 2026, November 3, 2025. The 2.8% COLA, the $184,500 contribution and benefit base, the retirement earnings test exempt amounts, and the quarter-of-coverage amount. Retrieved September 4, 2026; verified September 4, 2026.
12. 12. Internal Revenue Service, Rev. Proc. 2025-32 — 2026 inflation adjustments (§ 4.14 standard deduction; § 4.42 gift exclusion). The standard deduction amounts, the additional amounts for age or blindness, the $19,000 gift exclusion, and the $194,000 non-citizen-spouse exclusion. Retrieved September 4, 2026; verified September 4, 2026.

Revision history.

This tool reads the maintenance record and, for the tax figures, the Illinois income tax, federal, and annual records; the maintenance record's history is below.

September 7, 2026

First release: the Illinois maintenance guideline (the 33 1/3 percent less 25 percent formula, the 40 percent ceiling, the duration table, the $500,000 gate) on an approximation of the standardized net income, and the maintenance buyout comparison (present value of the stream at a discount rate, the stop-early allowance, the lump sum's monthly equivalent, and the crossover rate).

Canonical address: https://consideratecapital.com/tools/illinois-maintenance-calculator