Finance & Economics · FIRE & Retirement
FIRE Retirement Calculator
Calculate your Financial Independence, Retire Early (FIRE) number, years to retirement, and safe withdrawal rate based on your savings rate and annual expenses.
Calculator
Formula
The FIRE Number is the total portfolio value needed to sustain retirement withdrawals indefinitely. Annual Expenses is your expected yearly spending in retirement. SWR (Safe Withdrawal Rate) is typically 4% (0.04) per the Trinity Study. Annual Savings is the amount you save per year. r is the expected real annual return rate on your investments (typically 5–7% nominal). The Years to FI formula accounts for compound growth of your existing portfolio and ongoing contributions.
Source: Bengen, W.P. (1994). 'Determining Withdrawal Rates Using Historical Data.' Journal of Financial Planning. Trinity Study: Cooley, Hubbard & Walz (1998). 'Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable.' AAII Journal.
How it works
The cornerstone of FIRE planning is the Safe Withdrawal Rate (SWR), most commonly set at 4%. This figure, derived from William Bengen's 1994 analysis of historical stock and bond returns dating back to 1926, represents the maximum percentage of a retirement portfolio you can withdraw each year with a very high probability of never running out of money over a 30-year retirement horizon. The Trinity Study (1998) subsequently confirmed and expanded this finding, showing a 95%+ success rate for a 50/50 stock-bond portfolio over 30-year periods. Your FIRE Number is simply your expected annual retirement expenses divided by your SWR — for example, $40,000 in annual expenses divided by 4% (0.04) yields a FIRE Number of $1,000,000.
The Years to Financial Independence calculation uses a future value of a growing annuity formula that accounts for both your existing portfolio compounding at your expected real rate of return and your ongoing annual contributions. The formula is: Years = ln((FIRE Number × r / Annual Savings) + 1) / ln(1 + r), where r is the expected annual real return. This elegantly captures the snowball effect of compounding — as your portfolio grows, its earnings increasingly dwarf your annual contributions, dramatically accelerating your journey to FI. The real return rate (after inflation) is typically estimated between 5% and 7% for a diversified stock-heavy portfolio using long-run historical data from indexes like the S&P 500.
Your Savings Rate is arguably the single most powerful lever in FIRE planning, as research by Mr. Money Mustache and others demonstrates that the relationship between savings rate and years to retirement is nonlinear and dramatic. A person saving 10% of income may need 40+ years to retire, while someone saving 50% may achieve FI in just 17 years, and at 75% savings the timeline collapses to under 10 years. This is because a high savings rate simultaneously builds your portfolio faster and reduces your FIRE Number by conditioning you to live on less. The calculator computes your savings rate as annual savings divided by gross annual income, giving you an instant benchmark against FIRE community milestones.
Worked example
Consider Alex, a 30-year-old software engineer earning $100,000/year who spends $45,000/year and saves $40,000/year. Alex currently has $80,000 invested in a diversified index fund portfolio and expects a real annual return of 7% using the standard 4% safe withdrawal rate.
Step 1 — Calculate the FIRE Number: FIRE Number = $45,000 / 0.04 = $1,125,000. This is the total portfolio value Alex needs to retire.
Step 2 — Calculate the Savings Rate: Savings Rate = $40,000 / $100,000 = 40%. This is a strong savings rate that places Alex well within FIRE-achievable territory.
Step 3 — Calculate Years to FI: r = 0.07. Years = ln(($1,125,000 × 0.07 / $40,000) + 1) / ln(1.07) = ln((78,750 / 40,000) + 1) / ln(1.07) = ln(2.96875) / 0.06766 = 1.0878 / 0.06766 ≈ 16.1 years. Alex will reach financial independence at approximately age 46, having turned $80,000 and consistent $40,000/year contributions into over $1.125 million through the power of compound growth.
Step 4 — Current Portfolio Coverage: $80,000 × 4% = $3,200/year — this is the annual income Alex's current portfolio can already support, a motivating reminder that the journey has already begun.
Limitations & notes
The FIRE calculator uses several important assumptions that may not reflect your individual situation. The 4% rule was derived from 30-year retirement horizons — those planning for a 40- or 50-year early retirement may benefit from a more conservative SWR of 3% to 3.5%, as longer time horizons introduce more sequence-of-returns risk. The expected real return rate of 7% is a historical average for U.S. equities; future returns may be lower, particularly given current market valuations, and international portfolios may perform differently. The calculation assumes consistent annual savings contributions and does not model variable income, career interruptions, major expenses like healthcare or education, or the impact of taxes on withdrawals from tax-advantaged accounts. Inflation is implicitly handled by using real (inflation-adjusted) return rates and expressing expenses in today's dollars, but unexpected inflation spikes can erode purchasing power beyond what the model anticipates. Social Security benefits, pension income, rental income, or part-time work in early retirement can all meaningfully reduce your required FIRE Number and are not captured here. Always consult a qualified financial planner before making major retirement decisions.
Frequently asked questions
What is the FIRE number and how is it calculated?
Your FIRE number is the total investment portfolio value you need to retire sustainably — calculated by dividing your expected annual retirement expenses by your chosen Safe Withdrawal Rate (SWR). Using the standard 4% SWR, the formula is simply Annual Expenses × 25. For example, if you plan to spend $50,000 per year in retirement, your FIRE number is $1,250,000. This figure represents the point at which your portfolio's investment returns can fund your lifestyle indefinitely.
Is the 4% rule still valid for early retirement?
The 4% rule was validated for 30-year retirement horizons and remains a widely-used benchmark, but early retirees with 40–50 year timelines face greater sequence-of-returns risk and should consider a more conservative withdrawal rate of 3% to 3.5%. Research by Pfau and others using Monte Carlo simulations suggests that 3.5% provides a much higher confidence level for 40-year retirements. Many FIRE practitioners also use flexible spending strategies — reducing withdrawals in down market years — to safely extend the 4% rule into longer retirements.
What savings rate do I need to retire early?
Your savings rate is the primary driver of your years-to-retirement timeline. Saving 10% of income typically leads to retirement in approximately 40+ years (traditional retirement), while 25% cuts that to around 32 years. Hitting a 50% savings rate can achieve FI in roughly 17 years, and an aggressive 65–75% savings rate can achieve FI in under 10 years from a zero starting balance. The dramatic acceleration at high savings rates occurs because you simultaneously lower your FIRE number (by living on less) and increase the speed at which you accumulate assets.
What return rate should I use for my investment portfolio?
Most FIRE calculations use a nominal return rate of 7–10% for a U.S. stock-heavy portfolio, based on the long-run historical average of the S&P 500. However, it is better practice to use a real (inflation-adjusted) return rate of approximately 5–7% to express everything in today's dollars, avoiding the need to separately adjust for inflation. Conservative planners often use 5% real returns to build in a margin of safety, particularly given that future market returns may be lower than historical averages in some forecasting models.
Does Social Security affect my FIRE number?
Yes, significantly — Social Security benefits can substantially reduce the portfolio size you need to reach financial independence. If you expect to receive $18,000/year in Social Security benefits at age 62 or later, you can subtract that from your annual expenses before calculating your FIRE number, potentially reducing it by $450,000 (at the 4% rule). However, retiring early before becoming eligible for Social Security means you must fully self-fund those interim years, so many early retirees calculate two phases: a pre-Social Security phase and a post-Social Security phase, requiring careful planning.
Last updated: 2025-01-15 · Formula verified against primary sources.