FIRE Calculator: 4% Rule & Years to FI
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FIRE Calculator: 4% Rule & Years to FI
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Formula: FIRE Number = Annual Expenses / Safe Withdrawal Rate
Worked example — FIRE Number: $1,250,000 | ~18 years to FIRE | Savings rate: 37.5%
Formula
FIRE Number = Annual Expenses / Safe Withdrawal Rate
The 4% rule states that withdrawing 4% of your portfolio in year 1, then adjusting for inflation each year, has historically sustained portfolios for 30+ years (Trinity Study, 1998). This calculator shows your required portfolio = Annual Expenses / 0.04, projected depletion timeline at different withdrawal rates, and how changing the rate to 3% or 5% affects longevity.
Worked Examples
Example 1: Standard FIRE — $50k Expenses
Problem:$50,000 annual expenses, $100,000 saved, saving $30,000/year, 7% returns, 4% withdrawal rate.
Solution:FIRE Number: $50,000 / 0.04 = $1,250,000 Progress: $100,000 / $1,250,000 = 8% Savings rate: $30,000 / $80,000 = 37.5% Years to FIRE: ~18 years (with compound growth)
Result:FIRE Number: $1,250,000 | ~18 years to FIRE | Savings rate: 37.5%
Frequently Asked Questions
What is FIRE (Financial Independence, Retire Early)?
FIRE is a movement focused on extreme savings and investment to achieve financial independence much earlier than traditional retirement age. The core idea: save 50-70%+ of your income, invest aggressively, and retire when your investment portfolio can sustain your living expenses indefinitely. FIRE number = Annual Expenses / Safe Withdrawal Rate (typically 4%). With $50,000 annual expenses and 4% withdrawal rate, your FIRE number is $1,250,000.
What is the 4% rule?
The 4% rule (Trinity Study) states you can withdraw 4% of your portfolio in year one of retirement, then adjust for inflation annually, with a high probability (95%+) of not running out of money over 30 years. It assumes a 50/50 to 75/25 stock/bond allocation. Some FIRE advocates use 3.5% for extra safety (especially for 40-50 year retirements) or 5% for more aggressive spending. Your withdrawal rate is the inverse of your 'multiply by X' factor (4% = 25x expenses, 3% = 33x).
What are Lean FIRE, Fat FIRE, and Coast FIRE?
Lean FIRE: Retire with minimal expenses ($20-40k/year), often involving frugal living, geographic arbitrage, or van life. Fat FIRE: Retire with comfortable or luxury expenses ($100k+/year), requiring a much larger portfolio. Coast FIRE: Have enough invested that compound growth alone will reach your FIRE number by traditional retirement age — you still work but only to cover current expenses, not to save more. Barista FIRE: Semi-retired with part-time work for healthcare and spending money.
What does adjusting the withdrawal for inflation each year actually mean?
The rule sets only the first year's withdrawal as a percentage of the starting portfolio. Every year after that you take the previous year's dollar amount increased by inflation, not a fresh percentage of the current balance. The distinction is important: a fixed real withdrawal keeps your purchasing power constant but takes a rising share of a falling portfolio, which is precisely what makes an early bear market dangerous.
What is sequence-of-returns risk and why does it matter most at retirement?
It is the risk that poor returns arrive early rather than late. Two retirees can experience the same average return over thirty years and end with very different outcomes, because withdrawals taken during a downturn sell more units to raise the same real income, permanently shrinking the base that has to recover. That asymmetry is why the sustainable withdrawal rate is driven by the worst historical sequences rather than by the average, and why the first decade of retirement carries the most weight.
Why do longer retirements require a lower withdrawal rate?
The original work tested a 30-year horizon. Lengthen the period and every unfavourable historical sequence has more years in which to deplete the portfolio, so the rate that survives all of them falls. A 45 or 50-year retirement is closer to a perpetuity, where sustainability depends on withdrawing no more than the long-run real return net of fees. This is why many people planning a very early exit use a rate materially below 4%.
What is a dynamic or guardrails withdrawal strategy?
Instead of a fixed inflation-adjusted amount, a dynamic strategy links spending to portfolio performance: withdrawals are trimmed after a large drawdown and raised after strong years, often within preset upper and lower bands. Because it stops taking full withdrawals from a shrinking base, it tolerates a higher starting rate than a rigid rule, at the cost of variable income. The trade-off is between a predictable income and a more robust portfolio.
How does asset allocation affect the sustainable rate?
The original studies reported success rates across different stock and bond mixes, and the pattern is a compromise. Too little equity and the portfolio cannot outpace inflation over decades; too much and a severe early drawdown does the damage described by sequence risk. Mixes in the broad middle of the range historically supported the highest sustainable withdrawals. Allocation choices depend on your own circumstances and are worth discussing with a qualified adviser.
Is the 4% rule the same as living off dividends and interest?
No. A dividend or interest strategy spends only the income a portfolio distributes and never touches principal, so it is constrained by current yields. The 4% rule deliberately allows principal to be drawn down, treating total return as the source of spending and accepting that the balance may fall in some years. The rule generally permits a higher and more stable spending level than a yield-only approach, but it requires tolerance for a declining balance.
Does the rule already account for taxes and investment fees?
No, and this is a common misreading. Withdrawals fund your spending, your tax bill and any advisory or fund expenses, so all three come out of the same 4%. A recurring expense ratio is a direct subtraction from the return the portfolio can sustain, which is why cost matters disproportionately over a multi-decade horizon. Tax treatment depends on which account types you draw from and on your jurisdiction, so verify it with a tax professional.
References
Reviewed for accuracy by Sahil, Senior Finance & Tax Editor · Editorial policy
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