Actuarial cost is the estimated present value of all the future benefits a pension plan or insurance arrangement is obligated to pay, translated into the periodic contributions or reserves needed to fund those obligations over time. For a defined benefit pension plan, the number usually splits in two: the normal cost, which is what accrues for the current year of employee service, and any payment toward unfunded past obligations. It matters because it drives both the employer’s required cash contribution and the pension liability shown on the balance sheet, and those two figures rarely match.
What the Number Represents
A pension plan promising monthly checks to thousands of retirees over the next 30 or 40 years needs a way to measure that total commitment right now. Actuarial cost is that measurement. Two principles make the translation possible.
The first is the time value of money. A dollar the plan will pay in 2046 costs less than a dollar today, because money invested now will grow. Actuaries apply a discount rate to pull every future payment back to present value. The second is probability. Not every employee will survive to retirement, stay long enough to vest, or live to a particular age afterward. Mortality tables, turnover rates, and retirement-age assumptions adjust each projected payment by the likelihood it will actually occur.
The same underlying obligation gets measured twice for two different purposes. The funding cost determines how much cash the employer must contribute each year to satisfy federal minimums under the Employee Retirement Income Security Act.{1Office of the Law Revision Counsel. 29 U.S. Code 1082 – Minimum Funding Standards} The accounting cost determines the pension liability on the balance sheet under generally accepted accounting principles, specifically FASB Accounting Standards Codification Topic 715. Same promise, different rules, different numbers.
Assumptions That Drive the Calculation
Every actuarial cost figure is only as reliable as the assumptions behind it. Small changes in key inputs can swing the result by millions of dollars for a large plan.
Economic Assumptions
The discount rate is the single most powerful lever. A higher rate shrinks the present value of future payments and produces a lower liability. A lower rate does the opposite. For funding purposes, federal law requires single-employer plans to use three segment rates derived from 24-month averages of high-quality corporate bond yield curves, not the plan’s own expected investment returns.{2eCFR. 26 CFR 1.430(h)(2)-1 – Interest Rates Used To Determine Present Value} For 2026 plan years, those segment rates range roughly from 4.75% for benefits payable within five years to about 5.7% or higher for benefits payable beyond 20 years, depending on the applicable month chosen.{3Internal Revenue Service. Pension Plan Funding Segment Rates}
Accounting under ASC 715 uses a different discount rate: one that reflects the rate at which the pension obligation could effectively be settled, measured against returns on high-quality fixed-income investments such as corporate bonds rated Aa or higher. The salary increase assumption also matters for plans that base benefits on final or career-average pay, because higher projected raises mean larger future benefit checks.
Demographic Assumptions
Demographic assumptions project the human side: when employees will retire, how many will leave before vesting, and how long retirees will live. Mortality tables carry a lot of weight. For 2026 funding valuations, the IRS requires plans to use the static mortality tables specified in Notice 2025-40, built from updated base mortality rates and mortality improvement projections.{4Internal Revenue Service. Updated Static Mortality Tables for Defined Benefit Pension Plans for 2026} A separate unisex table blending 50% male and 50% female mortality rates applies when calculating the present value of certain lump-sum distributions.
Turnover assumptions reduce the projected obligation by accounting for workers who leave before earning full benefits. Retirement-age assumptions affect when payments begin. These inputs are typically drawn from the plan’s own experience studies, supplemented by industry data, and updated when actual experience drifts from what was projected.
Cost Methods That Spread the Total Across Years
Assumptions tell you the total size of the obligation. A cost method tells you how to spread that total across each year of an employee’s career. Two methods dominate pension practice, and they produce noticeably different annual cost patterns.
Projected Unit Credit
The projected unit credit (PUC) method assigns cost based on the specific benefit earned in each year of service. For a plan that pays 1.5% of final average salary per year of service, PUC calculates the present value of the benefit slice attributable to this year’s service, using projected rather than current salary. Because each year’s unit of benefit is discounted over a shorter remaining period as the employee ages, the normal cost under PUC starts relatively low for younger workers and grows over time. That rising pattern is the method’s defining feature.
GAAP accounting under ASC 715 generally requires a benefit-attribution approach consistent with PUC for salary-related plans, because it matches cost to the period in which benefits are earned. That alignment makes PUC the standard for balance-sheet reporting.
Entry Age Normal
The entry age normal (EAN) method takes the total projected benefit obligation and spreads it as a level percentage of pay, or a level dollar amount, from the employee’s hire date through retirement.{5Actuarial Standards Board. Entry Age Normal Actuarial Cost Method} Because the cost is leveled from the start, it produces more stable year-to-year contributions. Plan sponsors often prefer EAN for budgeting and cash-flow planning, and it is commonly used for funding valuations.
Both methods arrive at the same total cost over the life of the plan. The difference is timing. PUC pushes cost toward the later years of a career; EAN distributes it evenly. When a plan’s workforce is aging, PUC tends to produce higher near-term costs than EAN would for the same obligation.
What the Employer Has to Contribute
Federal law sets the floor. The minimum required contribution for a single-employer plan equals the target normal cost for the year, plus any shortfall amortization charge, plus any waiver amortization charge.{6Office of the Law Revision Counsel. 26 USC 430 – Minimum Funding Standards for Single-Employer Defined Benefit Pension Plans} If plan assets already equal or exceed the funding target, the minimum drops to the target normal cost reduced by the surplus.
The shortfall amortization charge is where underfunding gets expensive. When the funding target exceeds asset value, the difference creates a shortfall amortization base that must be paid off in level annual installments. The Pension Protection Act of 2006 originally set a seven-year schedule, but the American Rescue Plan Act of 2021 extended that to 15 years for plan years beginning after 2021. The longer window gives sponsors more breathing room on annual contributions, but the shortfall lingers on the books longer and accumulates more interest along the way.
Contributing more than the minimum in any year builds a credit balance that can offset future minimum contributions. Companies with strong cash flow sometimes front-load contributions during profitable years to create that cushion.
Why the Balance Sheet Number Differs From the Funding Number
The pension liability on a company’s balance sheet is not the same number the actuary uses for the funding contribution, even though both describe the same underlying promise. GAAP under ASC 715 typically requires a projected benefit obligation measured using a discount rate tied to high-quality corporate bonds rated Aa or above. The funded status reported on the balance sheet is the difference between that obligation and the fair value of plan assets.
Funding valuations use the three IRS segment rates and may apply different mortality and retirement assumptions.{3Internal Revenue Service. Pension Plan Funding Segment Rates} A plan can look reasonably well-funded for regulatory purposes yet show a significant liability on the balance sheet, or the other way around. Anyone evaluating corporate pension risk needs to understand both numbers and why they diverge.
Actuarial Gains and Losses
No set of assumptions perfectly predicts the future, so every year produces a gap between what the actuary expected and what actually happened. These gaps are actuarial gains and losses, and they are a normal part of running a plan.
An actuarial loss increases the plan’s obligation. Common causes: retirees living longer than the mortality table predicted, asset returns falling short of the assumed rate, or a decision to lower the discount rate to reflect current market conditions. An actuarial gain works in the other direction, driven by higher-than-expected investment returns, more employee turnover than projected, or an increase in the discount rate.
Under GAAP, these gains and losses do not hit the income statement all at once. ASC 715 allows companies to defer recognition into accumulated other comprehensive income and amortize the excess only when the cumulative net gain or loss exceeds 10% of the greater of the projected benefit obligation or the market-related value of plan assets. Amounts inside that corridor can remain unrecognized indefinitely. The smoothing prevents large swings in reported pension expense, but it also means the income statement can understate the plan’s true economic volatility.
What Happens if the Minimum Isn’t Paid
Missing the minimum required contribution triggers real financial consequences. The IRS imposes an excise tax of 10% of the aggregate unpaid minimum required contributions for a single-employer plan.{7Office of the Law Revision Counsel. 26 U.S. Code 4971 – Taxes on Failure To Meet Minimum Funding Standards} If the shortfall isn’t corrected within the taxable period, a second-tier tax of 100% of the unpaid amount applies. That is not a typo. Persistent underfunding is taxed dollar for dollar.
Multiemployer plans face a lower initial excise tax of 5% on their accumulated funding deficiency, but the same 100% second-tier penalty applies if the deficiency goes uncorrected. The penalties exist to make underfunding more expensive than funding, and most sponsors treat the minimum contribution as non-negotiable.
On top of that, every single-employer defined benefit plan pays premiums to the Pension Benefit Guaranty Corporation. For 2026, single-employer plans owe a flat-rate premium of $111 per participant regardless of funding level, plus a variable-rate premium of $52 per $1,000 of unfunded vested benefits, capped at $751 per participant.{8Pension Benefit Guaranty Corporation. Premium Rates} A fully funded plan pays only the flat rate. A badly underfunded plan with thousands of participants can face variable-rate premiums in the millions, which is a direct financial incentive to improve funded status beyond what the minimum contribution rules alone require.
Actuarial Cost Outside Pensions
The term travels. Life insurers, health insurers, and property-casualty companies all maintain reserves that represent the present value of future claims they expect to pay, and the underlying math is the same: discount future cash outflows to present value using appropriate interest rates, then adjust for the probability that each payment will actually come due. For a life insurance company, the actuarial reserve on a policy equals the present value of expected future benefit payments minus the present value of future premiums the policyholder will pay. The regulatory framework is different, since state insurance departments rather than federal agencies set reserve requirements, but the actuarial question is identical.