To calculate the Projected Benefit Obligation, you project each participant’s salary forward to retirement, apply the plan’s benefit formula using only the service they have earned so far, convert the resulting stream of future payments into a present value using a high-quality corporate bond discount rate, adjust for mortality and turnover, and then sum the individual results across every active, vested-terminated, and retired participant in the plan. That last part matters: the PBO is a participant-by-participant calculation rolled up to a plan total, not a single top-down formula. It is the pension liability measure required for balance sheet recognition under FASB’s Accounting Standards Codification 715.
What You Need Before You Start
A PBO calculation draws on three buckets of information. Missing or stale inputs in any of them will throw off the result.
Participant Data
For each person in the plan you need current salary, date of hire, credited years of service, and employment status: active, terminated with vested benefits, or already retired and collecting. HR records typically hold this, but the numbers have to be reconciled against the legal plan document to confirm vesting. Anyone who hasn’t met the vesting requirements drops out of the calculation entirely.
The Benefit Formula
The plan document controls the math. Most defined benefit plans use a variation of: a percentage, multiplied by years of credited service, multiplied by a final-average pay figure. A common example is 1.5% × years of service × average of the highest five consecutive years of earnings. The percentage and the averaging period vary widely, so pull them from the specific plan text rather than assuming.
Three Market-Driven Assumptions
Salary growth rate. This projects each employee’s pay to their expected retirement date. Actuaries build it from company history and broader compensation surveys, typically combining general inflation, productivity gains, and seniority-based raises.
Discount rate. Under ASC 715, the discount rate should reflect yields on high-quality fixed-income investments with durations matching the plan’s expected cash flows, which in practice means AA or higher corporate bonds. The IRS publishes separate segment rates for minimum funding calculations under IRC Section 430: for 2026 plan years those are 4.75% for the first segment, 5.25% for the second, and 5.74% for the third.1Internal Revenue Service. Pension Plan Funding Segment Rates Those segment rates drive funding, not the GAAP PBO directly, but they are a useful reference point for the shape of the yield curve.
Mortality. Life expectancy determines how long retirees will collect. The IRS requires specific static mortality tables for minimum funding valuations; the tables for 2026 plan years are the Section 430(h)(3)(A) Static Tables set out in Notice 2025-40.2IRS.gov. Updated Static Mortality Tables for Defined Benefit Pension Plans for 2026 For GAAP-based PBO work, actuaries often draw from tables published by the Society of Actuaries, which maintains an inventory of over 2,500 rate tables covering experience mortality, regulatory valuation, and population data.3Society of Actuaries. Actuarial Tables, Calculators and Modeling Tools Underestimating life expectancy understates the obligation.
The Five Steps, With Numbers
Once the inputs are in place, the mechanics run the same way for every participant. Repeat the sequence across the workforce and sum to get the plan-level PBO.
Step 1: Project the Salary to Retirement
Take the participant’s current pay and grow it at the assumed salary increase rate until expected retirement. An employee earning $100,000 today, assumed to receive 3% annual raises over 20 years to retirement, has a projected final salary of $100,000 × (1.03)20, or roughly $180,600.
Step 2: Apply the Benefit Formula Using Service Earned So Far
This is what the “projected” in PBO refers to. Use the projected retirement-age salary from Step 1, but only the years of service the employee has accumulated through the measurement date. With a formula of 1.5% × years × final salary, and 10 years of service on the books, the annual retirement benefit earned so far is 1.5% × 10 × $180,600 = $27,090. Today’s service applied to tomorrow’s salary is what separates the PBO from the Accumulated Benefit Obligation, which uses current pay only.
Step 3: Value the Retirement Payment Stream
Multiply the annual benefit by an annuity factor that reflects expected years of collection and the discount rate. Actuaries use mortality tables rather than a single fixed number for life expectancy, but for illustration: at a 5.25% discount rate over 20 years of collection, the annuity factor is roughly 12.2, so the value of expected payments measured at the retirement date is about $27,090 × 12.2 = $330,500.
Step 4: Discount Back to Today
That $330,500 sits 20 years in the future. Divide by (1 + discount rate) raised to the years remaining until retirement: $330,500 ÷ (1.0525)20 ≈ $118,900. That is this participant’s contribution to the PBO.
Step 5: Adjust for Turnover and Sum
Not everyone stays until retirement. Actuaries apply turnover probabilities pulled from the company’s historical departure rates. If cumulative probability of leaving before vesting or retirement age is 30%, the participant’s PBO contribution is reduced accordingly. Run the same five steps for every active participant, every vested terminated participant, and every retiree already collecting, then add the individual present values together. That total is the plan’s PBO.
How PBO Differs From ABO and VBO
Three pension liability measures show up in this territory, and confusing them changes the answer by a lot. The Accumulated Benefit Obligation uses current salaries only: what the plan would owe if every employee froze their pay today. The PBO projects salaries to retirement, so because most defined benefit formulas key off final or final-average pay, the PBO is almost always larger. The Vested Benefit Obligation is a subset of the ABO, limited to benefits an employee has a legal right to collect if they leave immediately. For balance sheet recognition under ASC 715, the PBO is the required measure. The ABO shows up mainly in minimum liability testing and in plan termination scenarios where future raises don’t apply.
Rolling the PBO Forward
The PBO is not a one-time number. It moves every reporting period, and understanding the moving parts is part of calculating it correctly at each measurement date.
Service Cost
Each year, participants earn another year of credited service under the benefit formula, which increases the obligation. The present value of the benefits earned during the current year is service cost. It is the largest controllable component and flows into operating expense.4FASB. Summary of Statement No. 87
Interest Cost
Because the PBO is a present value, it grows as each payment date moves one year closer. Interest cost equals the opening PBO multiplied by the discount rate. A $50 million opening PBO at a 5.25% discount rate produces roughly $2.625 million of interest cost for the year. It isn’t new benefit owed; it’s the unwind of the discount on the existing obligation.
Actuarial Gains and Losses
Actual experience never lines up perfectly with the assumptions. Employees retire earlier or later than expected, salary increases run higher or lower, and discount rates move with the bond market. A drop in the discount rate raises the present value of future payments and pushes the PBO higher; a rate increase does the opposite. The differences between expected and actual outcomes are actuarial gains and losses.
Plan Amendments
When a company retroactively increases (or, less often, decreases) benefits for past service, the change hits the PBO immediately as prior service cost. FASB requires delayed recognition on the expense side: the change goes first into other comprehensive income and is then amortized into net periodic pension cost over the average remaining service life of the affected employees.4FASB. Summary of Statement No. 87
Small shifts in the underlying assumptions can move the PBO by millions of dollars on a large plan. That sensitivity is why the discount rate, salary growth rate, and mortality table selections are the parts of the calculation that get scrutinized hardest, both by auditors and by the actuaries who sign the valuation.