FIRE Number Calculator (Retire Early)
FIRE (Financial Independence, Retire Early) lets you stop working when your invested portfolio can fund your lifestyle indefinitely. The classic rule: save 25× your annual expenses — at a 4% safe withdrawal rate, your money statistically lasts 30+ years. This calculator shows your target number, how many years away you are, and which FIRE variant fits your goals.
When to use this calculator
- Determine your exact FIRE number based on current annual spending
- Project how many years until you reach financial independence
- Compare Lean FIRE, Standard FIRE, Fat FIRE, and Coast FIRE targets
- Calculate the gap between your current portfolio and your FI target
- Model how increasing monthly savings accelerates your retirement date
- Evaluate whether a lower expected real return changes your timeline
How it works
2 min readWhat is FIRE?
FIRE (Financial Independence, Retire Early) is a strategy where your invested portfolio generates enough passive income to cover your living expenses indefinitely. The standard approach uses the 25× rule: save 25 times your annual expenses at a 4% safe withdrawal rate, allowing you to retire when your portfolio reaches that target number.
How the FIRE Number Is Calculated
The FIRE number is the portfolio size at which you can withdraw your annual expenses indefinitely without running out of money.
FIRE Number = Annual Expenses × Multiplier
Multipliers:
Lean FIRE → 20× (5.0% SWR)
Standard → 25× (4.0% SWR)
Fat FIRE → 33× (3.0% SWR)The 4% Safe Withdrawal Rate (SWR) comes from the Trinity Study (1998, updated 2011, 2024), which backtested US stock/bond portfolios from 1926 onward and found a 4% withdrawal rate had a ~95% success rate over 30-year periods.
Years to FI Formula
To project how long it takes to grow your current portfolio P to the target T with monthly contributions c and monthly real return r = (real_return / 100) / 12:
If P >= T: years = 0
Otherwise, solve for n (months):
T = P × (1 + r)^n + c × [(1 + r)^n − 1] / r
n = ln[(T + c/r) / (P + c/r)] / ln(1 + r)
years = n / 12When r = 0, the formula simplifies to n = (T − P) / c.
Coast FIRE
Coast FIRE answers: how large must my portfolio be today so that, with zero additional contributions, it grows to my Standard FIRE number by retirement age?
Coast FIRE Number = FIRE Number / (1 + r_annual)^(retirement_age − current_age)If your current portfolio already exceeds this value, you can stop contributing and still retire on time.
Worked Example
| Input | Value |
|---|---|
| Annual expenses | $50,000 |
| Current portfolio | $150,000 |
| Monthly savings | $2,500 |
| Real return | 6% |
| Variant | Standard (25×) |
| Current age | 32 |
Limitations & When NOT to Apply
Frequently asked questions
What is the FIRE number?
Your FIRE number is the total invested portfolio you need to retire. It equals your annual expenses multiplied by a factor based on your chosen withdrawal rate — 25× for the standard 4% rule. A household spending $60,000/year needs $1,500,000.
Where does the 25× rule come from?
The Trinity Study (Cooley, Hubbard & Walz, 1998) backtested portfolios from 1926–1995 and found that withdrawing 4% of an initial portfolio annually, adjusted for inflation, sustained a 50/50 stock-bond portfolio for 30 years in ~95% of historical scenarios. 1 ÷ 4% = 25.
What is the difference between Lean, Standard, and Fat FIRE?
Lean FIRE uses 20× (5% SWR) for frugal lifestyles under ~$40,000/year. Standard FIRE uses 25× (4% SWR) for typical middle-class spending. Fat FIRE uses 33× (~3% SWR) for $100,000+/year lifestyles with extra safety margin.
What is Coast FIRE?
Coast FIRE is the portfolio size where, if you stop contributing entirely today, compound growth alone will reach your full FIRE number by traditional retirement age (~65). Once you hit Coast FIRE, you only need to cover current expenses — not save extra.
Should I use nominal or real return?
Use real return (after inflation). A typical US diversified index portfolio has returned ~9.5% nominally and ~6.5% real over the last 50 years. Using 6–7% real is a common conservative assumption for planning purposes.
Does the 4% rule work for early retirees?
The Trinity Study modeled 30-year periods. Retiring at 40 means a 50+ year horizon. For early retirees, many researchers suggest using a 3–3.5% SWR, which corresponds to a 28–33× multiplier, to handle the longer time frame and sequence risk.
Are taxes included in this calculation?
No. Withdrawals from tax-deferred accounts (Traditional 401k, IRA) are taxed as ordinary income. Roth accounts are tax-free. Your actual spending target should account for your expected tax burden in retirement — often adding 10–25% to pre-tax withdrawal needs.
What if I have Social Security or a pension?
Subtract guaranteed income from your annual expenses before calculating. If you expect $15,000/year from Social Security and spend $50,000, your portfolio only needs to cover $35,000 — reducing your FIRE number from $1,250,000 to $875,000 (25× rule).
What annual return should I assume?
Vanguard's 2026 10-year forecast projects 4.2–6.2% real for a global 60/40 portfolio. Using 5–6% real is a cautious baseline. If you invest 100% in equities, 6–7% real is commonly used, though future returns may differ from historical averages.
How does monthly savings rate affect my timeline?
Savings rate is the biggest lever. Doubling monthly contributions from $1,000 to $2,000 can cut 5–8 years off a typical 15-year path to FIRE, depending on current portfolio and return assumptions. Small increases in savings matter far more than chasing higher returns.