How ERISA's Accrual Rules Actually Build a Pension

ERISA — the Employee Retirement Income Security Act of 1974 — establishes the federal floor for how a private-sector defined-benefit pension plan must credit workers with retirement benefits over time. The law does not set the size of any benefit; it sets the rules by which a plan is permitted to build, withhold, and ultimately pay that benefit. Those rules are called accrual standards, and they govern the rate at which a participant earns a share of the eventual pension, year by year, from the first day of employment through separation.

This piece covers the accrual machinery specifically: how ERISA defines a year of service, which accrual methods a plan may legally use, how vesting schedules interact with accrued benefits, and where the system produces results that participants do not anticipate. What ERISA covers more broadly — fiduciary duties, funding requirements, disclosure obligations — is a separate layer of the statute, addressed in the piece on what ERISA actually requires of a pension plan.

How Benefit Accrual Is Credited Under ERISA's Three Permitted Methods

ERISA Section 204 requires that a defined-benefit plan use one of three accrual methods, each of which sets a minimum rate at which a participant must earn a share of the projected benefit. The three methods are: the 3% method, the 133⅓% rule, and the fractional accrual method. A plan may be more generous than any of these floors, but it may not be less generous.

Under the 3% method, a participant must accrue at least 3% of the projected normal retirement benefit for each year of participation, up to a maximum of 33⅓ years. This means a plan using this method fully credits a participant after 33⅓ years of service, and no single year of participation may produce an accrual below that 3% floor.

Under the 133⅓% rule, the accrual rate in any plan year may not exceed 133⅓% of the accrual rate in any earlier plan year. This prevents a plan from back-loading benefits heavily into late career years — a design that would technically satisfy a lifetime projection while delivering almost nothing to workers who leave before reaching long tenures. The rule is tested annually and applies to the benefit rate, not the dollar amount, so plans with career-average formulas must apply it carefully.

Under the fractional accrual method, a participant who has worked a fraction of the years needed to reach normal retirement age has earned at least that same fraction of the projected benefit. A worker with 10 years of service under a plan that requires 30 years for full retirement has accrued at least 10/30ths — one-third — of the full projected benefit. This method is the most commonly used in practice because it maps naturally onto the final-average-pay and career-average formulas that most plans employ.

The underlying benefit formula determines what number those fractions are applied to. A typical final-average-pay formula multiplies a benefit multiplier (often expressed as a percentage per year of service) by years of credited service and by a final average salary figure, usually the average of the highest three or five consecutive years of compensation. The mechanics of that multiplication are detailed in the piece on how a defined-benefit pension formula calculates a payout. ERISA's accrual rules do not dictate the formula's inputs; they dictate the minimum rate at which the formula's output must be credited to the participant over time.

A "year of service" under ERISA is defined as a 12-month period in which a participant completes at least 1,000 hours of service. Plans may use either the plan year or the anniversary of the hire date as the measuring period, but the 1,000-hour threshold is a federal floor — a plan may not require more hours to credit a year of participation. Hours of service include hours actually worked and hours for which the employee is entitled to payment even without working, such as vacation, illness, and jury duty.

Who Administers Accrual Tracking and What Federal Oversight Applies

The plan administrator — typically the employer or a committee appointed by the employer for single-employer plans, or a joint board of trustees for multiemployer plans — is responsible for tracking each participant's years of credited service, calculating the accrued benefit at each plan year-end, and maintaining the records that support both figures. ERISA imposes the fiduciary standard on anyone who exercises discretionary authority over plan administration, which includes decisions about how service is credited and how the accrual formula is applied to ambiguous employment situations.

The Department of Labor's Employee Benefits Security Administration (EBSA) is the primary federal agency that enforces ERISA's participation, vesting, and accrual standards. EBSA has authority to audit plan records, investigate participant complaints, and bring civil actions against plan administrators who fail to comply with accrual requirements. The Internal Revenue Service also has jurisdiction over defined-benefit plans because the tax-qualified status of the plan — which allows employers to deduct contributions and participants to defer taxation — depends on the plan satisfying ERISA's and the Internal Revenue Code's parallel accrual and coverage rules.

When a single-employer defined-benefit plan terminates with insufficient assets to pay all accrued benefits, the Pension Benefit Guaranty Corporation (PBGC) steps in as the federal insurer. The PBGC is a government corporation established by ERISA itself. It pays guaranteed benefits up to statutory maximum limits, which are adjusted annually. For plan terminations in 2024, the maximum guaranteed monthly benefit for a participant retiring at age 65 is $7,107.95. Benefits accrued above that ceiling are not insured. The PBGC guarantee also phases in for benefits that have been in place for fewer than five years at the time of plan termination, so recently improved accrual formulas may not be fully covered.

Multiemployer plans — those maintained under collective bargaining agreements covering workers from multiple employers — are covered by a separate PBGC program with different, generally lower, guarantee limits. The financial condition of multiemployer plans became a significant policy issue in the 2010s and 2020s, and the American Rescue Plan Act of 2021 created a special financial assistance program administered by the PBGC for the most distressed multiemployer plans.

Where Accrual Rules Break Down or Produce Unexpected Results

Cliff vesting and the near-miss problem. ERISA permits plans to use either cliff vesting or graded vesting schedules. Under cliff vesting, a participant who leaves before completing the required years of service — currently a maximum of three years for employer contributions in most plan types — forfeits the entire accrued benefit. A participant who has accrued three years of service minus one day receives nothing. The accrual rules and the vesting rules are separate mechanisms: a benefit can be fully accrued under the formula but not yet vested, meaning the participant has earned a calculated amount but has no legal right to receive it upon separation.

Back-loading within the 133⅓% rule. The 133⅓% rule prevents extreme back-loading but does not eliminate it. A plan can still be structured so that the accrual rate in early years is materially lower than in later years, as long as no single year's rate exceeds 133⅓% of any prior year's rate. Workers who leave after moderate tenures — ten or fifteen years — may find their accrued benefit is a much smaller fraction of the full projected benefit than a simple proportional calculation would suggest.

Break-in-service rules and the one-year holdout. ERISA's break-in-service rules allow a plan to disregard pre-break service in certain circumstances. Under the "one-year holdout" rule, a plan may exclude service before a break if the break equals or exceeds the greater of five years or the participant's pre-break service. A worker who leaves after three years, returns after six years, and expects those three early years to count may find that the plan legally disregards them entirely.

What ERISA does not cover. A question that arises frequently — sometimes phrased as "does ERISA apply to Medicare" or "what does ERISA cover with respect to Medicare" — reflects a common misreading of the statute's scope. ERISA governs private-sector employee benefit plans, including pension plans and welfare benefit plans such as employer-sponsored health coverage. Medicare is a federal health insurance program administered under Title XVIII of the Social Security Act; it is not an employer benefit plan and is not subject to ERISA's requirements. The two programs interact in specific, limited ways — for example, ERISA's preemption provisions affect how states can regulate employer health plans, and Medicare's secondary payer rules determine which coverage pays first when an active employee also has Medicare — but ERISA does not govern Medicare's benefit structure, eligibility, or administration. Similarly, ERISA does not cover government employer plans (federal, state, or local) or church plans, which are exempt from the statute's requirements.

Lump-sum conversions and mortality assumptions. When a plan offers a lump-sum distribution option in lieu of the annuity, the conversion uses an interest rate and mortality table specified under the Internal Revenue Code. Changes in interest rates between the time a participant accrues a benefit and the time the lump sum is calculated can produce a lump-sum amount that is substantially lower than the actuarial present value of the annuity at the time of accrual. This is not a violation of ERISA's accrual rules; it is a consequence of how present-value arithmetic responds to rising interest rates.

What the Annual Benefit Statement Shows — and What It Omits

ERISA Section 105 requires plan administrators of defined-benefit plans to provide participants with a pension benefit statement at least once every three years, or upon request. The statement must show the participant's total accrued benefit and the vested portion of that benefit as of the statement date. It must also include a general description of the plan's normal retirement benefit and, if applicable, an explanation of any permitted disparity (integration with Social Security) that affects the benefit calculation.

What the statement typically does not show is the projected benefit at normal retirement age under various future-service assumptions. Unlike the Social Security Statement, which projects future benefits under assumed earnings scenarios, the ERISA-required pension benefit statement reports only the accrued benefit to date — the amount earned based on service and compensation already recorded. A participant reading only the accrued benefit figure on a statement issued at age 45 will see a number that reflects perhaps 15 or 20 years of service, not the full career projection the plan's formula would produce at age 65.

The statement also does not show the PBGC guarantee limit applicable to the participant's benefit. If the accrued benefit exceeds the PBGC maximum, nothing on the statement flags that portion as uninsured. Participants in plans with high benefit formulas — particularly those covering highly compensated employees — may have accrued amounts that exceed the PBGC ceiling without any indication of that exposure appearing on their benefit statement.

For plans that offer both annuity and lump-sum options, the statement shows the accrued benefit in its annuity form. The lump-sum equivalent, if one exists, is calculated at the time of distribution using then-current interest rates, and that figure does not appear on periodic statements. The gap between what a statement shows and what a lump sum would actually deliver at distribution is therefore not visible in the statement itself.

ERISA's accrual framework is a set of minimum floors, not a benefit design — it constrains how slowly a plan may credit benefits and how long a plan may withhold vesting, but the formula, the multiplier, and the compensation base are all set by the plan document itself. The statutory machinery establishes the boundaries; what sits inside those boundaries varies considerably from plan to plan.

Note: This explains how a retirement system works. It is not financial, tax, or legal advice, it is not specific to any individual's retirement, and it is not a substitute for a licensed financial, tax, or legal professional. Rules, ages, and dollar limits change by year — check the cited sources.