Docket 23-1209
M & K Employee Solutions, Inc. v. Trustees of IAM Nat. Pension
DecidedMay 21, 2026
9-0unanimous decision
Source: CourtListener.
Court allows pension funds to set actuarial assumptions after the measurement date for withdrawal liability
What it does
The Court holds that ERISA sections 1391 and 1393 do not require actuarial assumptions to be adopted on or before the measurement date. Actuaries may select assumptions after that date, so long as the hard factual data used in the calculation (like plan assets and beneficiary counts) is fixed as of the measurement date.
Who benefits
Multiemployer pension plans and their trustees, who retain flexibility to adopt updated actuarial assumptions after the measurement date when calculating a withdrawing employer's liability.
Who is affected
Employers who withdraw from underfunded multiemployer pension plans, who may face withdrawal liability calculated using assumptions adopted after the measurement date, potentially increasing the amount they owe.
Practical impact
Pension plans can continue to update discount rates and other actuarial assumptions after the close of the plan year, potentially increasing withdrawal liability for employers who leave underfunded plans. Employers challenging these assessments must rely on arbitration to argue that particular assumptions are unreasonable or not the actuary's best estimate, rather than arguing that late-adopted assumptions are categorically barred.
Majority reasoning
The Court reasoned that the phrase "as of" in Section 1391 fixes the reference date only for hard factual data about the plan, such as the number of beneficiaries and asset values, not for actuarial assumptions, which are predictive judgments rather than observable facts. It noted that Section 1393 groups assumptions with "methods," confirming they are tools for calculating unfunded vested benefits rather than facts frozen in time. The Court found no deadline in Section 1393's text requiring reasonableness and "best estimate" assumptions, and applying the interpretive presumption from Russello v. United States, concluded that Congress's inclusion of a deadline elsewhere in the statute (Section 1399) but not here was intentional. It also reasoned that requiring assumptions to be locked in before the measurement date could force actuaries to rely on stale data, undermining the statutory requirement that assumptions reflect the actuary's "best estimate." The Court rejected petitioners' reliance on Section 1394's antiretroactivity rule for "plan rules or amendments," noting that provision does not cover actuarial assumptions and that Congress's choice not to extend a similar rule to assumptions should not be overridden by courts. Finally, the Court rejected petitioners' manipulation concerns as unaddressed by their own proposed rule and inconsistent with the principle that policy concerns cannot override the best reading of the statutory text, noting that unreasonable assumptions remain challengeable in arbitration.
Constitutional question
Whether ERISA requires a multiemployer pension plan's actuary to select the assumptions (like the discount rate) used to calculate an employer's withdrawal liability on or before the statutory measurement date, rather than afterward.