FIRE Calculator — Financial Independence Number
Calculate your FIRE number using the 4% safe withdrawal rate, find your months to financial independence, Coast FIRE number, and see how savings rate affects your timeline.
Quick Presets
What Is the FIRE Calculator — Financial Independence Number?
FIRE (Financial Independence, Retire Early) is based on one simple insight: if your investments can sustain your annual spending indefinitely, you no longer need to work for money. The math is built on the Safe Withdrawal Rate — the maximum annual withdrawal percentage that historically has not depleted a diversified portfolio over a 30-year retirement.
- ›The 4% rule — From the 1994 Bengen study and the Trinity Study (1998): withdrawing 4% of a 60/40 portfolio in year 1 and adjusting for inflation thereafter succeeded in 95%+ of 30-year periods since 1926. However, early retirees with 40–50 year horizons need a more conservative rate (3–3.5%).
- ›Savings rate is the fastest lever — Increasing your savings rate from 15% to 50% doesn't just accumulate more — it also reduces the annual spending your portfolio needs to sustain. Both effects compound simultaneously.
- ›Coast FIRE — The point at which existing savings, allowed to compound without further contributions, will grow to your full FIRE number by your target retirement age. Once you hit Coast FIRE, you only need to cover current expenses — not save beyond them.
- ›Lean vs Fat FIRE — Lean FIRE targets a frugal retirement (often <$40k/yr). Fat FIRE targets a comfortable or luxurious retirement ($80k–$150k+/yr). The FIRE number scales linearly with spending.
Formula
FIRE Number
FIRE Number = Annual Expenses / Safe Withdrawal Rate
At 4% SWR: FIRE = Annual Expenses × 25
Years to FIRE
Years = ln((FIRE − Portfolio) / (FIRE − Portfolio + Savings/r)) / ln(1+r)
Coast FIRE Number
Coast FIRE = FIRE Number / (1 + r)^years_to_retirement
Savings Rate Impact
Higher savings rate → lower required portfolio (spend less) + faster accumulation
| SWR | FIRE Multiplier | 30-yr Success Rate* | Best for |
|---|---|---|---|
| 3.0% | 33× | ~98% | Early retirees with 40+ year horizon |
| 3.5% | 28.6× | ~95% | Conservative; very long retirement |
| 4.0% | 25× | ~95% | Trinity Study baseline (30-yr horizon) |
| 4.5% | 22.2× | ~85% | Moderate; some flexibility needed |
| 5.0% | 20× | ~75% | Aggressive; requires spending flexibility |
How to Use
- 1Enter annual expenses: Your current annual spending, or the spending level you want to sustain in retirement. This is the most critical input.
- 2Enter current portfolio: Total investable assets (brokerage, IRA, 401k). Exclude home equity and illiquid assets unless they're part of your plan.
- 3Enter annual savings: How much you add to investments each year. This is gross savings — contributions plus employer match.
- 4Set expected return rate: Real (inflation-adjusted) return. 5–7% is reasonable for a diversified stock/bond portfolio. Use real returns to avoid adjusting for inflation separately.
- 5Set safe withdrawal rate: 4% is the standard baseline for 30-year retirements. Use 3–3.5% for retirements longer than 30 years.
- 6Review FIRE number and timeline: The calculator shows your FIRE number, months until you reach it, and Coast FIRE number.
- 7Test different scenarios: Adjust spending, savings rate, or return assumptions to see sensitivity. Cutting $10k/year in spending has a double benefit.
Example Calculation
$60,000/yr expenses, $150,000 portfolio, $30,000/yr savings, 7% return, 4% SWR
FIRE Number (4% SWR): $60,000 / 0.04 = $1,500,000
Savings rate: $30,000 / ($30,000 + $60,000) = 33%
Gap to FIRE: $1,500,000 − $150,000 = $1,350,000
Years to FIRE (7% real): ~18.3 years
If savings rate → 50% ($45k/yr saved, $45k/yr expenses):
New FIRE Number: $45,000 / 0.04 = $1,125,000
Years to FIRE: ~12.4 years (5.9 years faster)
Coast FIRE @ age 25 for age 55 retirement (30 years):
$1,500,000 / 1.07^30 = $197,200 (Coast FIRE number)
Savings rate cuts years, not just months
Raising savings rate from 33% to 50% in this example shaves nearly 6 years off the timeline. The dual effect: more invested AND less spending to fund in retirement. Every percentage point of savings rate translates to roughly 0.5 fewer years of work — asymmetrically powerful at higher rates.
Understanding FIRE — Financial Independence Number
The Research Behind the 4% Rule
William Bengen (1994) found that a 50%+ equity portfolio with annual 4% withdrawals (inflation-adjusted) survived every 30-year period from 1926–1976 using historical return data. The Trinity Study (Cooley, Hubbard, Walz, 1998) expanded this work and found approximately 95% success rates for 30-year horizons with 4% withdrawal and a 75% stock / 25% bond allocation. Importantly: the original research assumed a 30-year retirement, not the 40–50 year retirements common in early FIRE cases.
The Sequence of Returns Problem
The 4% rule's biggest risk is not average returns but the sequence of returns early in retirement. A major market downturn in years 1–5 of retirement, combined with ongoing withdrawals, can permanently impair a portfolio even if long-term returns are adequate. Strategies to mitigate: maintain a 1–3 year cash/bond buffer, cut discretionary spending in down years (flexible spending), and consider part-time income or a bond tent in early retirement years.
FIRE Variants by Spending Level
- ›Lean FIRE: Annual expenses under $40,000. FIRE number under $1M at 4% SWR. Possible in lower cost-of-living areas or with very intentional frugality.
- ›Regular FIRE: $40k–$80k annual expenses. FIRE number $1M–$2M. Achievable for most high earners with 10–20 year timelines.
- ›Fat FIRE: Over $100k/yr expenses. FIRE number $2.5M+. Targets a comfortable lifestyle with no significant spending restrictions in retirement.
- ›Barista FIRE: Partial retirement — portfolio covers most needs, part-time work or side income covers the rest. Reduces the FIRE number and provides health insurance access.
Healthcare Before 65
Early retirees face a healthcare coverage gap between leaving employer insurance and Medicare eligibility at 65. ACA marketplace plans (healthcare.gov) are the primary option. Subsidies are income-based — early retirees with low reported income may qualify for substantial subsidies. Roth conversion ladders and capital gains management can keep MAGI low enough to qualify, making healthcare cost manageable but requiring careful tax planning.
Disclaimer
FIRE projections are mathematical models based on assumed constant returns. Actual returns vary, and past performance does not guarantee future results. The 4% rule is based on US historical data; international diversification introduces different return profiles. Consult a fee-only financial planner for personalized retirement planning. References: Bengen 1994 (AAII); Trinity Study — Cooley, Hubbard & Walz (1998); IRS Retirement Plans.
Frequently Asked Questions
Is the 4% rule still valid for early retirees?
The original 4% rule (Bengen 1994, Trinity Study 1998) was designed for 30-year retirements. Early retirees with 40–50 year horizons need a more conservative rate.
- ›30-year horizon: 4% withdrawal rate shows ~95% historical success rate.
- ›40-year horizon: 3.5% is more appropriate — slightly lower to reduce depletion risk.
- ›50-year horizon: 3–3.25% is widely recommended for very early retirees (retiring in 30s–40s).
- ›Flexible spending: FIRE retirees who can cut spending 10–20% in bad market years significantly improve success rates.
Most FIRE retirees also have options for part-time income, consulting, or low-effort income — which provides a natural buffer that improves the real-world outcome beyond what fixed-spending models predict.
What is Coast FIRE and how does it differ from regular FIRE?
Coast FIRE is the portfolio size where, if you stop saving and let it compound, it will reach your full FIRE number by your target retirement age — without any additional contributions.
- ›Once you hit Coast FIRE, you only need to earn enough to cover current living expenses.
- ›You no longer need to save for retirement — just cover day-to-day costs.
- ›Lower-stress milestone: many people reach Coast FIRE 8–12 years before full FIRE.
- ›Formula: Coast FIRE = FIRE Number ÷ (1 + real return rate)^years until retirement.
Coast FIRE is a meaningful psychological and financial milestone — it decouples your current lifestyle from your retirement security, allowing more career flexibility even years before full retirement.
How does inflation affect the FIRE calculation?
There are two valid approaches. This calculator uses real returns to avoid the need for separate inflation adjustments.
- ›Real return approach (this calculator): subtract inflation from your nominal return — e.g., 7% nominal − 3% inflation = 4% real return.
- ›FIRE number stays in today's dollars; no annual adjustment needed.
- ›Nominal approach: use nominal returns (7%) but increase spending target by inflation each year.
- ›Both approaches are equivalent when done correctly; the real return method is simpler.
Key implication: using a 7% return in this calculator while inflation is 3–4% overstates your real portfolio growth. Use 4–5% to be conservative if inflation is elevated.
Should I include Social Security in my FIRE calculation?
Social Security meaningfully reduces your required FIRE portfolio, but treatment depends on your confidence in future benefits.
- ›$20,000/yr SS benefit reduces your FIRE number by $500,000 at a 4% SWR.
- ›Conservative approach: exclude SS entirely or haircut to 70–75% of projected benefit.
- ›Early retirees: limited working years may substantially reduce AIME and SS benefit amount.
- ›Claiming age: SS benefit is maximized at 70 — FIRE retirees often bridge the gap with portfolio withdrawals.
For younger FIRE retirees (retiring before 50), excluding Social Security from the primary calculation and treating it as a bonus provides the most conservative and defensible plan.
What portfolio allocation is best for FIRE?
FIRE frameworks generally recommend high equity during accumulation, transitioning to a balanced allocation near and in early retirement.
- ›Accumulation phase: 80–100% equity — time horizon is long, volatility is tolerable, growth matters most.
- ›Early retirement: 70–80% equity — still need long-term growth for a 40–50 year horizon.
- ›Bond tent strategy: raise bond allocation from 60 to 70–80 in the 5 years before retirement as sequence risk buffer, then reduce back.
- ›Trinity Study finding: portfolios with 75%+ equity outperformed lower-equity portfolios over most 30-year periods.
The greatest risk in early retirement is the sequence of returns — a major downturn in years 1–5 can permanently impair the portfolio. A cash or bond buffer for the first 2–3 years of expenses is a common mitigation strategy.