FIRE Calculator: How to Use It
Most FIRE calculators assume your portfolio is the only income source in retirement. This one treats your pension as the centerpiece. A $2,500 monthly pension is worth $750,000 in portfolio savings under the 4% rule. This page explains how the calculator accounts for that.
What this calculator does
The pension-aware FIRE Calculator computes your FIRE number with and without pension income, shows the dollar value your pension contributes to financial independence, models the bridge period before pension and Social Security start, runs a 30-year year-by-year retirement portfolio simulation with pension and Social Security start dates built in, and stress-tests the plan against a conservative 5% return scenario. It also includes a current-trajectory analysis showing whether you're on track to hit your target portfolio by your planned retirement age.
The FIRE number without pension is the standard calculation: annual spending times 25. The FIRE number with pension is (annual spending minus annual pension income) times 25. The difference between those two numbers is the dollar value your pension provides toward financial independence. Public employees who see this number for the first time often find they're closer to FIRE than they thought.
What each input means
Annual spending in retirement
Your estimated total annual expenses in retirement, in today's dollars. Include housing, food, transportation, healthcare, travel, and any other recurring costs. Don't include taxes as a line item unless you've calculated them explicitly; the calculator works in gross income terms. If you're uncertain, the Bureau of Labor Statistics Consumer Expenditure Survey shows median annual spending for households aged 55 to 74 ranges from roughly $48,000 to $58,000 depending on household size and region.
Current portfolio balance
The total of all investable assets: 401(k), 403(b), 457(b), IRA, Roth IRA, and taxable brokerage accounts. Don't include home equity or other illiquid assets unless you plan to liquidate them for retirement income. The current balance feeds the trajectory analysis that shows whether you're on pace to hit your FIRE number by your target retirement age.
Annual savings rate
Total annual contributions to all retirement and taxable accounts, including employer matching contributions. This is the amount added to your portfolio each year between now and your target retirement date. The trajectory analysis uses this figure alongside your current balance and assumed return to project your portfolio at retirement.
Target retirement age
The age at which you want to stop working. The calculator uses this to determine the number of accumulation years remaining, compute the bridge period length before pension and Social Security begin, and check whether your projected portfolio at that age equals or exceeds your FIRE number.
Annual pension income
Your expected annual pension payment in today's dollars, starting at the age your pension begins. If your pension won't start until a few years after you retire, enter the amount it will pay when it starts, not when you stop working. The calculator handles the gap between retirement and pension start separately through the bridge period calculation. If you have a FERS pension, use the FERS Pension Calculator to estimate your annuity, then bring that number here.
Pension start age
The age at which your pension begins paying. For FERS employees, this is typically your MRA for standard retirement. For teachers and state employees, it varies by plan rules. If your pension starts immediately at retirement, set this equal to your target retirement age. If there's a gap, set it to the actual start age, and the calculator will model the bridge period between those two ages.
Estimated annual Social Security
Your expected Social Security benefit at the claiming age you plan to use, in today's dollars. Get this from your Social Security Statement at ssa.gov/myaccount. Use the age-specific estimate, not the full retirement age figure if you plan to claim at a different age. Set the Social Security start age to match when you intend to file. Early retirees who plan to delay Social Security to 67 or 70 to maximize that benefit should set this age accordingly; the calculator models the income gap between pension start and Social Security start.
Expected portfolio return
The annual rate of return you expect on your investment portfolio during both the accumulation phase and retirement. A balanced 60/40 portfolio has historically averaged 6 to 7 percent annually over long periods. The calculator runs the base case at your entered return and a conservative scenario capped at 5%. Both results appear in the output so you can see how much your plan depends on return assumptions.
Understanding the outputs
The FIRE number comparison shows three figures: your standard FIRE number (annual spending times 25), your pension-adjusted FIRE number (spending gap times 25), and the pension's portfolio equivalent (the dollar value by which your pension reduces the required portfolio). If your pension pays $36,000 per year and you spend $80,000, the pension covers $36,000, leaving a $44,000 gap. At 25x, your FIRE number is $1.1 million instead of $2 million. The pension is worth $900,000 in portfolio terms.
The bridge period analysis shows the total portfolio needed to fund the years between retirement and when guaranteed income begins covering a meaningful share of expenses. If you retire at 55 and your pension starts at 58, the bridge period is three years of 100% portfolio-funded living. The calculator shows how much portfolio those three years consume and whether your projected balance at retirement can absorb it.
The year-by-year table tracks your portfolio balance through retirement, showing how it changes as pension income begins, as Social Security starts, and as inflation adjustments accumulate. Look for any year where the portfolio balance approaches zero. That's the failure point. If the conservative 5% scenario reaches zero, your plan needs adjustment: more savings, later retirement, lower spending, or earlier Social Security claiming.
Lean FIRE vs. fat FIRE with a pension
Lean FIRE targets minimal spending, often $40,000 per year or below for individuals. Fat FIRE targets high-income retirement, typically $80,000 to $150,000 or more. A pension changes the math for both. A lean FIRE retiree with a $2,000 monthly pension spending $40,000 per year has a $16,000 gap and needs only $400,000 in portfolio assets. A fat FIRE retiree spending $120,000 with the same pension has an $96,000 gap and needs $2.4 million. The pension provides more relative value to lean FIRE targets because it covers a larger fraction of total spending.
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Frequently asked questions
What is the 4% rule and where does it come from?
William Bengen's 1994 research found that withdrawing 4% of a portfolio's initial balance annually, adjusted for inflation each year, survived every 30-year retirement period from 1926 forward in a roughly 50/50 stock and bond portfolio. The Trinity Study confirmed this in 1998. Your FIRE number is 25 times annual spending. For retirements longer than 30 years, 3% to 3.5% provides higher historical success rates.
How does a pension reduce my FIRE number?
Your portfolio only needs to cover the gap between spending and guaranteed income. A $30,000 annual pension on $80,000 of spending leaves a $50,000 gap. At 25x, that requires $1.25 million instead of $2 million. The pension is worth $750,000 in portfolio terms. Public employees with pensions often need 30 to 50 percent less in savings than private sector workers with identical spending.
What is the bridge period and why does it matter?
The bridge period is the time between when you stop working and when pension or Social Security income begins. During the bridge, 100% of expenses come from the portfolio at a higher effective withdrawal rate. A portfolio sufficient for 4% withdrawals over 30 years may not survive a 5-year bridge where it funds 100% of expenses. The calculator models bridge years separately and shows the additional portfolio required.
What is the conservative scenario?
A stress test with the portfolio return assumption capped at 5%. If the plan still works at 5%, you have cushion against bad early returns. If it only works at 7% or 8%, the plan depends on above-average market performance from the start of retirement, which is the riskiest possible assumption for a FIRE retiree facing decades of withdrawals.
Can I retire early if I haven't reached pension eligibility yet?
Yes, but the bridge period before pension eligibility becomes the binding constraint. The calculator models a multi-phase retirement: bridge years at 100% portfolio funding, then pension-plus-portfolio years, then full retirement income with Social Security added. Each phase affects the portfolio differently. The year-by-year table shows whether the portfolio survives all three phases.