Pension Calculator

The formula behind most pension plans

A defined benefit pension pays a monthly amount for life, and the size of that amount comes from three numbers: years of service, a multiplier the plan sets, and the average of your highest earning years. Multiply the three together and you have the annual benefit.

Annual pension = years of service x multiplier x final average salary.

The final average salary, often shortened to FAS, is usually the average of your highest 3 or 5 consecutive years. Some plans use the last 5 years, some use the best 3, and a few average the whole career. The plan document names the rule, and it changes the answer more than most people expect: a promotion in the final two years can lift the average by thousands of dollars a year for the rest of your life.

The multiplier is a percentage per year of service. A 2% plan credits you with 2% of your final average salary for every year you worked, so 30 years lands at 60%. That percentage is the single most valuable line in the plan booklet, and it is fixed at hire in most public plans and negotiable in some private ones.

The third input, years of service, is the one you control. Buying service credit, working two more years, or waiting out a furlough all move the number, and each year adds the multiplier times the salary to the annual benefit for life.

Worked example: 30 years at 2% of $65,000

A teacher, a meter reader or a county engineer with 30 years in a 2% plan and a $65,000 final average salary gets the following.

• 30 x 2% = 60% of the final average salary
• 60% x $65,000 = $39,000 a year
• $39,000 ÷ 12 = $3,250 a month

Sixty percent of pay is the number to hold onto. That is the replacement rate, and it is what the pension is designed to deliver after a full career. The same formula at 25 years gives 50% and $32,500 a year, and at 35 years it gives 70% and $45,500 a year.

Five more years of service is worth $6,500 a year for life in this example, plus whatever salary growth those years bring. Over a 20 year retirement that is $130,000, which is why the last few years before retirement are the most expensive ones to leave early.

Change the multiplier to 1.5% and the same 30 years pays 45% of $65,000, or $29,250 a year. Change it to 2.5% and the pension is 75% of pay, or $48,750. A half point of multiplier is worth $9,750 a year here, which is more than most people save in a 401(k) in a year.

Multipliers by plan type

Multipliers cluster by the kind of employer, because they are set by statute or by bargaining rather than by the market. The ranges below are the ones that show up in plan summaries; the exact figure is always in your own booklet.

The federal figure comes from the Office of Personnel Management's FERS computation rules: FERS pays 1.0% per year for most employees, and 1.1% for someone who retires at 62 or later with at least 20 years. That tenth of a percent is worth 3% of pay at 30 years, and it is the reason some federal employees work to 62 rather than 60.

Social Security does not fit the table because its benefit formula is progressive. It replaces a larger share of a low earner's pay than a high earner's, using bend points rather than a flat multiplier. Treat any single percentage for Social Security as a rough comparison, not a calculation.

Retiring early: what the discount costs

Almost every pension plan reduces the benefit when you start before normal retirement age. The common rule in public plans is 0.5% per month, which is 6% a year, and it applies for every month between your start date and normal age.

Take the $39,000 pension and claim it at 60 with a normal retirement age of 65. That is 60 months early, and 60 x 0.5% = 30%, so the pension becomes 70% of $39,000, which is $27,300 a year or $2,275 a month.

The reduction is permanent. It is not repaid when you reach 65, and cost of living adjustments apply to the smaller base, so the gap widens over time. What you get in exchange is 60 monthly checks before the other path starts: 60 x $2,275 = $136,500 collected by age 65.

Whether that trade wins depends on how long you live. The full pension is $11,700 a year more than the reduced one, and $136,500 ÷ $11,700 = 11.7, so you break even at about 77. Live past 77 and claiming at 65 pays more in total; die before it and the early claim wins. A spouse's benefit and your health history belong in that decision, and so does the fact that a dollar at 60 is worth more to most people than a dollar at 80.

Some plans use 4% or 5% a year instead of 6%, and a few use an actuarial table that varies with age. Check the rate before you run the numbers, because a 5% rule cuts the early penalty by about a sixth.

How Social Security cuts an early claim

Social Security uses its own arithmetic, and it is worth knowing because most people have both a pension and a Social Security benefit. The Social Security Administration reduces a retired worker benefit by 5/9 of 1% for each month before full retirement age, up to 36 months. Beyond 36 months the reduction is 5/12 of 1% per month.

Full retirement age is 67 for anyone born in 1960 or later. Claim at 62 and you are 60 months early: 36 x 5/9 = 20%, plus 24 x 5/12 = 10%, for a total reduction of 30%. A $2,000 primary insurance amount becomes $1,400 a month, and that 30% cut follows you for life.

Waiting past 67 works in the other direction. Delayed retirement credits add 8% a year for anyone born in 1943 or later, up to age 70, so a benefit claimed at 70 is 124% of the full amount.

The 2026 cost of living adjustment is 2.8%, which turns a $2,000 benefit into $2,056. That adjustment applies to whatever benefit you are receiving, reduced or not, which is another reason the early cut compounds.

One rule change matters for anyone with a public pension. The Windfall Elimination Provision and the Government Pension Offset used to reduce Social Security for people who also earned a pension from work that Social Security did not cover. The Social Security Fairness Act, signed on January 5, 2025, repealed both, and the SSA page on the Fairness Act explains what changed.

None of this replaces your own Social Security statement. The agency's my Social Security account shows your actual earnings record and an estimate at each claiming age, and it is the only number worth planning around.

Inflation and what $39,000 buys in 20 years

A pension that never changes loses value every year. At 3% inflation, prices double in about 23 years, and a benefit frozen at $39,000 buys less each January even though the check is the same size.

Twenty years at 3% divides the purchasing power by 1.03 to the twentieth power, which is 1.806. So $39,000 in 2046 buys what $21,593 buys today, a loss of 45% of the value.

A cost of living adjustment fixes part of this. A 2% COLA against 3% inflation still loses about 1% a year in real terms: after 20 years the purchasing power is 82.3% of the starting value, or $32,087. A full 3% COLA holds the line, which is why the presence or absence of a COLA clause is worth more than a slightly higher starting benefit.

Run the comparison before you trade one for the other. A plan offering $36,000 with a full COLA overtakes $39,000 with no COLA in purchasing power during year 3, and the gap widens every year after that.

Inflation is not a constant, which is the weak point in any projection. The 2022 spike ran above 8%, and the decade before it averaged under 2%, according to the Bureau of Labor Statistics CPI series. Use 3% as a central case, then check 2% and 4% to see how much the answer moves.

COLA, vesting and the fine print

Vesting is the number of years before the employer's contributions belong to you. Five years is common in private plans, and 5 to 10 in public ones. Leave at year 4 and you may get only your own contributions back, sometimes with interest and sometimes without.

The COLA clause is the second thing to read. Some plans guarantee a fixed 3%, some cap the adjustment at 2% or at the CPI with a ceiling, and many private plans have none at all. A capped COLA behaves like a flat benefit in a high inflation year, which is exactly when you need it.

Then look at the survivor option. A joint and survivor election usually cuts the pension by 10% to 25% so that a spouse keeps 50% or 100% of it after you die. That is not a fee; it is insurance priced into the benefit, and skipping it leaves a surviving spouse with nothing from the plan.

Finally, check the early retirement subsidy. Some plans waive part of the reduction for people who hit a combination of age and service, such as 30 years at any age or 80 total points. Those rules can be worth more than a year of extra service, and they are easy to miss in a summary plan description.

What this calculator cannot tell you

The arithmetic here is the standard formula, and it matches the one in most summary plan descriptions. It is still an estimate, not a benefit statement. Real plans add rules for disability retirement, military service credit, divorce orders, refunds of contributions and minimum benefits that no single formula captures.

For a Social Security figure, use the statement in your my Social Security account rather than this page. The agency's estimate uses your full earnings record, and its early and delayed claiming rules are applied to your own primary insurance amount. For a workplace pension, the plan administrator can produce an official estimate, usually at no cost and often within a few weeks.

This is a planning tool, not financial, tax or legal advice. Pension formulas, COLA clauses and early retirement rules change, and the plan document controls in every dispute. Confirm any figure that matters with your plan administrator or a qualified professional before you make a decision.