Docket 23-1209
M & K Employee Solutions, Inc. v. Trustees of IAM Nat. Pension
DecidedMay 21, 2026
Source: CourtListener.
Pension funds may use actuarial assumptions adopted after the withdrawal measurement date
What it does
ERISA does not require pension plan actuaries to select their actuarial assumptions — such as the discount rate used to calculate a plan's unfunded vested benefits — on or before the statutory measurement date. Actuaries may adopt those assumptions after the measurement date, so long as the assumptions are reasonable and reflect the actuary's best estimate of the plan's anticipated experience. The ruling resolves a split between the D.C. Circuit and the Second Circuit, siding with the D.C. Circuit's interpretation.
Who benefits
Multiemployer pension funds and their actuaries, who now have flexibility to select or update actuarial assumptions after the measurement date, potentially using more current data when calculating how much a departing employer owes.
Who is affected
Employers who withdraw from underfunded multiemployer pension plans, who may face higher withdrawal liability assessments if a pension fund adopts a lower discount rate after the measurement date but before completing its calculations.
Practical impact
Multiemployer pension funds may now finalize the actuarial assumptions used to calculate a departing employer's withdrawal liability after the measurement date has passed, as long as those assumptions are reasonable and data-grounded. Employers who withdraw from underfunded pension plans cannot automatically insist that the fund use whatever discount rate or other assumptions were in place before the measurement date. Employers who believe a fund's post-measurement-date assumptions are unreasonable retain the right to challenge them through arbitration.
Majority reasoning
The majority held that ERISA's "as of" language in §1391 fixes the date for hard factual data about the plan — such as the number of beneficiaries and the value of assets — but does not set a deadline for selecting actuarial assumptions. The Court reasoned that actuarial assumptions are not observable facts about a plan; they are predictive tools used to perform calculations, and ERISA's own text groups them with "methods" rather than factual inputs. The Court further found that §1393, the section that actually governs actuarial assumptions, imposes no deadline whatsoever, and that Congress's decision to include a deadline in a different section of the statute while omitting one in §1393 signals that the omission was intentional. The majority also noted that requiring assumptions to be locked in before the measurement date could force actuaries to use outdated data, undermining §1393's requirement that assumptions reflect the actuary's "best estimate." Finally, the Court rejected the employers' policy argument about manipulation risk, noting that the statute already provides safeguards — including an arbitration process to challenge unreasonable assumptions — and that policy concerns cannot override the best reading of the statutory text.
Constitutional question
Does ERISA's requirement that withdrawal liability be calculated "as of" the last day of the plan year preceding an employer's withdrawal set a deadline by which actuaries must select the assumptions used in that calculation?
Precedent changed
The ruling effectively resolves and rejects the Second Circuit's contrary holding in National Retirement Fund v. Metz Culinary Management, Inc., 946 F.3d 146 (2020), which had required interest rate assumptions to be adopted on or before the measurement date, though the Court does not formally overrule that lower-court decision.