The years decide the share of the pension.

The facts, in one place.

Six quotable sentences on dividing a pension in an Illinois divorce.

1. Pension benefits acquired by or participated in by either spouse after the marriage and before the judgment are presumed marital property, whatever the plan and whoever earned them (750 ILCS 5/503(b)(2)).
2. Illinois courts divide a defined-benefit pension one of two ways, both approved in In re Marriage of Hunt, 78 Ill. App. 3d 653 (1979): an immediate offset of its present value against other property, or reserved jurisdiction, under which the former spouse takes a share of each benefit check when it is paid.
3. Under reserved jurisdiction the marital portion of each check is the coverture fraction: months of plan participation during the marriage over total months of participation at retirement. The former spouse customarily takes half the marital portion; the share is negotiable.
4. Example: five years in the plan before the wedding, fifteen married, ten more until retirement, a $4,000 monthly pension. The fraction is 15/30, so $2,000 of each check is marital and the former spouse receives $1,000. Frozen at the divorce instead, on the $2,200 earned by then, the share would be $825.
5. The fraction is applied to the benefit as actually paid at retirement, post-divorce raises and service included; the growing denominator, not a frozen benefit, is what protects the employee spouse (In re Marriage of Richardson, 381 Ill. App. 3d 47 (2008)).
6. A public pension (SERS, SURS, TRS, IMRF, the Chicago funds) is divided only by a QILDRO under 40 ILCS 5/1-119, which needs the member's written consent if the member joined on or before July 1, 1999; a private plan by a QDRO under ERISA § 206(d)(3) and IRC § 414(p). The decree alone moves nothing.

The fraction as service continues.

How the former spouse's share shrinks as the employee keeps working, on the same benefit.

How the fraction works.

A pension is deferred pay, and the part of it earned during the marriage is marital property whoever's name is on the plan. Hunt gave Illinois courts two ways to divide it. The first values the pension at dissolution and offsets it against other property, which needs an actuary and a spouse able to give up something else of equal worth. The second, reserved jurisdiction, waits: when the pension is paid, the former spouse takes a share of each check equal to the months of participation during the marriage over the total months of participation at retirement. The share of the marital portion is customarily half, and the decree can set another figure.

Under the usual Illinois order the fraction is applied to the benefit as actually paid, so post-divorce raises and years of service raise the marital portion in dollars while the growing denominator shrinks the fraction; Richardson holds that this, and not a benefit frozen at the divorce, is the reserved-jurisdiction method. A decree can instead freeze the benefit at the divorce date, which is the comparison the calculator shows. Either way the decree moves nothing by itself: a public pension needs a QILDRO in the statutory form (with the member's consent if the member joined on or before July 1, 1999), a private plan a QDRO the administrator accepts, and each is drafted by counsel.

Methodology.

1. Inputs. Years in the plan before the marriage, years married while in the plan (to the filing), years in the plan after the filing until retirement, the monthly benefit at retirement in today's dollars, the benefit earned as of the divorce (blank to estimate it evenly), and the former spouse's share of the marital portion.
2. The fraction. Years during the marriage over total years in the plan at retirement: the Hunt coverture fraction, in years rather than months, so whole years only.
3. The shares. The benefit times the fraction is the marital portion; the former spouse's share of that is the monthly figure; the employee keeps the rest of the check.
4. The frozen alternative. The fraction as of the divorce (years during over years to the divorce) applied to the benefit earned by then, from the statement or, if blank, the retirement benefit prorated evenly over service; then the same share.
5. Validation. The 5 / 15 / 10 case pinned (50 percent marital, $1,000 to the former spouse; frozen, 75 percent of $2,200, $825), a career wholly inside the marriage (fraction 1), the even-accrual estimate, and a 40 percent share. A transcription error fails the build.
6. Not modeled. Months (the tool takes whole years), breaks in service, early-retirement reductions, survivor annuities and the election that funds them, cost-of-living increases, defined-contribution accounts (divided by balance, not fraction), the immediate-offset valuation, and the plan's own QDRO or QILDRO procedures and forms. Educational, not advice.

Sources.

1. 1. United States Code (Cornell LII), 26 U.S.C. § 414(p) — Qualified domestic relations order defined. What a qualified domestic relations order is: a court order under state domestic relations law that assigns part of a participant's plan benefit to a spouse, former spouse, child, or dependent, and the requirements it must meet for the plan to honor it. Retrieved September 6, 2026; verified September 6, 2026.
2. 2. Illinois Appellate Court, First District (CourtListener), In re Marriage of Hunt, 78 Ill. App. 3d 653 (1st Dist. 1979). The two ways an Illinois court divides a pension: an immediate offset of its present value at dissolution, or reserved jurisdiction, under which the non-employee spouse receives a share of each benefit payment equal to the months of plan participation during the marriage over the total months of participation at retirement, the coverture fraction that carries the case's name. Retrieved September 7, 2026; verified September 7, 2026.
3. 3. Illinois Appellate Court, First District (CourtListener), In re Marriage of Richardson, 381 Ill. App. 3d 47 (1st Dist. 2008). That under the reserved-jurisdiction method the marital fraction is applied to the benefit as actually paid at retirement, including increases from post-dissolution service and salary, the fraction itself shrinking as service continues; a decree that instead freezes the benefit at the dissolution date is the alternative the tool shows for comparison. Retrieved September 7, 2026; verified September 7, 2026.
4. 4. Illinois General Assembly, 750 ILCS 5/503(b)(2) — Pension benefits acquired during the marriage are presumed marital property. That all pension benefits, including those under the Illinois Pension Code, defined benefit and defined contribution plans, IRAs, and non-qualified plans, acquired by or participated in by either spouse after the marriage and before the judgment are presumed marital property, and that division of a public pension is enforceable under Section 1-119 of the Pension Code. Retrieved September 7, 2026; verified September 7, 2026.
5. 5. Illinois General Assembly, 40 ILCS 5/1-119 — Qualified Illinois Domestic Relations Orders. That benefits under the state's public retirement systems (SERS, SURS, TRS, IMRF, the Chicago funds, and the rest) are divided only by a QILDRO in the statutory form, as a fixed dollar amount or a percentage set out in a QILDRO Calculation Court Order; and that a QILDRO against a member who began participating on or before July 1, 1999 is not effective without the member's written consent (m). Retrieved September 7, 2026; verified September 7, 2026.
6. 6. United States Code (Cornell LII), 29 U.S.C. § 1056(d)(3) (ERISA § 206(d)(3)) — Qualified domestic relations orders. That the anti-alienation rule for private plans yields to a qualified domestic relations order, and what such an order must state; the parallel definition is § 414(p) of the Internal Revenue Code. Retrieved September 7, 2026; verified September 7, 2026.

Revision history.

This tool reads the divorce record; its history is below.

September 7, 2026

Added the pension division sources for the marital-share tool: Hunt and Richardson (the coverture fraction under reserved jurisdiction), 503(b)(2) (pension benefits presumed marital), 40 ILCS 5/1-119 (QILDRO for public pensions, the pre-July-1999 consent rule), and ERISA § 206(d)(3) (QDRO for private plans).

September 6, 2026

First release of the divorce record for the retirement-account split and the house-or-IRA comparison: the IRA transfer rule, the QDRO exception, the § 1041 carryover basis, and the home exclusion after a divorce.

Canonical address: https://consideratecapital.com/tools/marital-share-of-a-pension