ERISA Withdrawal Liability: Actuarial Assumptions Need Not Be Adopted by the Measurement Date

1. Introduction

M & K Employee Solutions, LLC, et al. v. Trustees of the IAM National Pension Fund (608 U.S. ___ (2026)) addresses a recurring technical question with major financial consequences in the multiemployer pension plan (“MPP”) system: when must a plan’s actuary select the actuarial assumptions used to calculate an employer’s withdrawal liability under ERISA?

Petitioners—four employers—withdrew from the underfunded IAM National Pension Fund in 2018. ERISA fixes the measurement date for valuing a plan’s unfunded vested benefits (“UVBs”) as the last day of the plan year preceding withdrawal (here, December 31, 2017). The Fund, however, used a lower discount rate (6.50%) adopted in January 2018—after the measurement date—rather than the 7.50% discount rate previously used. Arbitrators sided with the employers, holding that assumptions had to be “in effect” on the measurement date. The District Courts and the D.C. Circuit reversed, creating a split with the Second Circuit’s contrary approach in National Retirement Fund v. Metz Culinary Mgmt., Inc..

The Supreme Court granted certiorari to resolve that circuit split and determine whether ERISA’s “as of” valuation requirement imposes a deadline for selecting actuarial assumptions.

2. Summary of the Opinion

Justice Jackson, writing for a unanimous Court, held that ERISA provisions governing withdrawal liability calculation—29 U.S.C. §§ 1391 and 1393—do not require actuarial assumptions to be selected on or before the measurement date. The Court reasoned:

  • Section 1391’s requirement to measure UVBs “as of” the measurement date fixes the relevant factual inputs (the “hard data”), but does not freeze predictive actuarial judgments.
  • Section 1393, which directly regulates actuarial assumptions, contains no textual deadline; instead it demands assumptions be “reasonable” and reflect the actuary’s “best estimate.”
  • Statutory structure reinforces the conclusion: Congress imposed a timing link in another provision concerning amortization assumptions, but did not do so in §1393.
  • Policy concerns about manipulation cannot overcome the statute’s text; employers’ protections lie in arbitration challenges to “unreasonable” assumptions.

3. Analysis

3.1. Precedents Cited

The Court’s interpretive method is strongly textualist, with multiple citations supporting the proposition that courts should not add statutory conditions Congress omitted.

United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337

Cited in the syllabus note to clarify that a syllabus is not part of the Court’s opinion. While not substantive to the ERISA question, it frames the reader’s use of the syllabus and reinforces that the binding analysis is in the opinion itself.

Connolly v. Pension Benefit Guaranty Corporation, 475 U. S. 211, 214 (1986)

Used to situate ERISA as a “comprehensive regulation for private pension plans.” This background supports the Court’s insistence that any additional timing rule must come from statutory text, not from judicial interpolation in a complex and comprehensive scheme.

Concrete Pipe & Products of Cal., Inc. v. Construction Laborers Pension Trust for Southern Cal., 508 U. S. 602, 605 (1993)

Provides the definition and characteristics of an MPP (multiple contributing employers; maintained pursuant to collective bargaining). The citation underlines why withdrawal liability is central to MPP stability: without withdrawal liability, the plan’s funding burden can be shifted to remaining employers.

Milwaukee Brewery Workers' Pension Plan v. Jos. Schlitz Brewing Co., 513 U. S. 414, 416-418 (1995)

Serves two roles. First, it explains the purpose of withdrawal liability—preventing insolvency upon employer exit. Second, it is cited for the “as of” measurement-date feature embedded across §1391 methods. The Court leverages this framework to separate (i) the statutory valuation date from (ii) the timing of performing the calculation and selecting tools used to perform it.

Romag Fasteners, Inc. v. Fossil Group, Inc., 590 U. S. 212, 215 (2020)

A key interpretive anchor: the Court “generally do[es] not read limitations into statutes that do not appear in their text.” Applied here, it blocks petitioners’ attempt to derive an implied “deadline” for adopting assumptions from §1391’s “as of” phrasing or from background anti-retroactivity intuitions.

Russello v. United States, 464 U. S. 16, 23 (1983)

Supports an expressio unius / structural inference: where Congress includes specific language in one section but omits it in another, the omission is presumed intentional. The Court applies Russello twice:

  • Congress tied amortization-period assumptions to “the most recent actuarial valuation” in §1399(c)(1)(A)(ii), but did not impose a similar timing restriction in §1393.
  • Congress enacted an anti-retroactivity provision for “plan rule or amendment” in §1394(a), but did not extend that rule to actuarial assumptions in §1393.

Patel v. Garland, 596 U. S. 328, 346 (2022)

Used to reject policy-driven statutory rewriting: “policy concerns cannot trump the best interpretation of the statutory text.” This is the Court’s answer to the manipulation argument—whatever the policy merits, Congress provided the “reasonable”/“best estimate” standard and arbitration review as the constraint.

Becerra v. Empire Health Foundation, for Valley Hospital Medical Center, 597 U. S. 424, 434 (2022)

Justifies consulting specialist materials (here, Actuarial Standards of Practice) when a statute is “addressed to specialists.” The Court uses this to support its characterization of actuarial assumptions as “tools” selected for a particular measurement purpose, rather than “facts” fixed and “in effect” on a date.

National Retirement Fund v. Metz Culinary Mgmt., Inc., 946 F. 3d 146, 152 (2020)

Identified as the contrary Second Circuit rule that assumptions “must” be adopted on or before the measurement date. The Supreme Court’s decision effectively disapproves that timing requirement, resolving the split by aligning federal law with the D.C. Circuit’s interpretation.

3.2. Legal Reasoning

(a) The meaning of “as of” in §1391: fixing facts, not freezing predictive tools

The Court treats §1391’s “as of” phrase as a temporal reference for the valuation target—not a deadline for every component that might be used to produce the valuation. Relying on usage sources (including W. Follett, Modern American Usage), the Court explains that “as of” assigns an event to one time and recognizes it at another. That understanding fits the parties’ shared premise that computations often occur after the measurement date.

The critical move is categorization:

  • Hard data (beneficiary counts, asset values) are facts about the plan and must be “as of” the measurement date.
  • Actuarial assumptions (discount rate, mortality, investment returns) are predictive judgments used to translate hard data into a present-value estimate; they are not “observable facts” and thus are not the kind of input that can meaningfully be “in effect” on a date in the way petitioners asserted.

The Court’s reading is reinforced by ERISA’s own drafting: §1393 groups “assumptions” with “methods,” implying both are valuation tools “used” to determine UVBs rather than pre-existing “facts.”

(b) §1393’s “best estimate” standard and the absence of a deadline

Section 1393 directly governs actuarial assumptions for withdrawal liability and imposes substantive standards—“reasonable,” reflecting plan experience and expectations, and the actuary’s “best estimate.” It imposes no timing requirement. Applying Romag Fasteners, Inc. v. Fossil Group, Inc., the Court refuses to insert one.

The Court then uses structure (via Russello v. United States) to show Congress knew how to impose a timing tether when it wanted to—most notably in §1399(c)(1)(A)(ii)’s link to the “most recent actuarial valuation” for amortization assumptions—yet did not do so for withdrawal-liability assumptions in §1393.

Finally, the Court gives a functional explanation tightly tied to the text “best estimate”: information relevant to what is true as of the measurement date may become available only later. A strict “adopt-by-date” rule could force reliance on stale information and thereby undermine the statutory demand for the actuary’s best estimate.

(c) Rejection of the anti-retroactivity analogy and the manipulation policy argument

Petitioners invoked §1394(a), which bars post-withdrawal “plan rule or amendment” changes from affecting withdrawal liability. The Court treats this as a textual dead end: actuarial assumptions are not “plan rules or amendments,” and Congress did not extend §1394’s anti-retroactivity logic to §1393.

On manipulation concerns, the Court’s response has two components:

  • A pre-measurement adoption deadline would not eliminate manipulation because actuarial discretion exists before the date as well.
  • Under Patel v. Garland, policy concerns cannot override statutory text; Congress chose the constraints (“reasonable,” “best estimate”) and the enforcement mechanism (arbitration challenges, including for “unreasonable” assumptions under §1401(a)(3)(B)(i)).

3.3. Impact

Doctrinal impact: a clear federal rule on timing

The decision establishes that ERISA does not require withdrawal-liability assumptions to be adopted by the measurement date. This removes a major source of timing-based challenges and resolves a circuit split in favor of the D.C. Circuit’s approach, rejecting the Second Circuit’s measurement-date adoption requirement from National Retirement Fund v. Metz Culinary Mgmt., Inc..

Practical impact: potentially higher liabilities and more focus on “reasonableness”

Because the discount rate heavily drives UVB present value, allowing post-measurement adoption can materially affect assessed withdrawal liability, as the Fund’s shift from 7.50% to 6.50% illustrates. After this decision, disputes are likely to shift from timing arguments (“adopted too late”) to merits arguments: whether assumptions were “reasonable” and truly the actuary’s “best estimate.”

Litigation frontier left open

The Court expressly “leave[s] that question for another day” regarding whether assumptions must be based only on information available as of the measurement date. That reservation signals likely future litigation about the permissible use of post-date information (e.g., whether later-released data about pre-date conditions may be considered, and how to draw the line between learning and hindsight).

Governance and compliance effects for plans and actuaries

Plans may feel greater flexibility to update assumptions in response to evolving macroeconomic conditions, and actuaries may document their “best estimate” rationale with greater care, anticipating arbitration scrutiny. Employers, correspondingly, may invest more heavily in actuarial rebuttal evidence in arbitration rather than relying on a timing “freeze” rule.

4. Complex Concepts Simplified

  • Multiemployer Pension Plan (MPP): A pension plan funded by multiple employers, typically under collective bargaining agreements.
  • Withdrawal liability: The amount an employer must pay when it exits an underfunded MPP—meant to cover its share of the plan’s underfunding so remaining employers are not stuck with the bill.
  • Unfunded vested benefits (UVBs): The gap between (i) the present value of vested benefits owed and (ii) the current value of plan assets.
  • Measurement date: The statutory valuation date for UVBs (generally the last day of the plan year before the year of withdrawal).
  • Discount rate: The assumed interest rate used to convert future benefit payments into a present value. Lower discount rate → higher present value of liabilities → higher UVBs → higher withdrawal liability.
  • “As of”: Sets the date that the valuation is aimed at (which facts are being valued), but does not necessarily control when calculations or selection of valuation tools occur.
  • Actuarial assumptions as “tools”: Not “facts” like asset values, but predictive judgments chosen to perform a valuation consistent with professional standards and ERISA’s “best estimate” requirement.
  • Arbitration review: ERISA routes many withdrawal-liability disputes to arbitration, where employers may challenge assumptions as “unreasonable.”

5. Conclusion

M & K Employee Solutions establishes a clear rule: ERISA’s “as of” measurement-date requirement fixes the valuation’s reference date for plan facts, but it does not impose a deadline for selecting actuarial assumptions. By grounding the analysis in statutory text and structure—especially §1393’s “best estimate” standard and the absence of a timing restriction—the Court resolves the circuit split and redirects future disputes toward whether assumptions are reasonable and reflect the actuary’s best estimate, rather than when those assumptions were adopted.