FIRE Calculator: How to Find Your Financial Independence Number
Financial Independence, Retire Early — FIRE — is built on a deceptively simple idea: save and invest enough money that your investment returns cover your living expenses forever. Once you reach that point, working becomes optional. The amount of money you need to get there is called your FIRE number, and it is more achievable than most people think.
This guide explains exactly how to calculate your FIRE number, walks through the math behind the 4% rule and Rule of 25, compares different types of FIRE, and shows you how your savings rate — not your income — determines when you can retire.
The formula: Rule of 25 and the 4% rule
Your FIRE number is calculated using the Rule of 25: multiply your expected annual expenses in retirement by 25. That is it. The Rule of 25 is the inverse of the 4% safe withdrawal rate — if you withdraw 4% of your portfolio each year, it should last indefinitely based on historical market returns.
The formula looks like this:
If you spend $40,000 per year → FIRE number is $1,000,000
If you spend $60,000 per year → FIRE number is $1,500,000
If you spend $80,000 per year → FIRE number is $2,000,000
The 4% rule originates from William Bengen's 1994 research, later expanded by the Trinity Study. The research examined every 30-year period in US market history and found that a 4% initial withdrawal rate (adjusted annually for inflation) survived in the vast majority of scenarios without the portfolio running out of money.
Is the 4% rule still valid in 2026?
The 4% rule remains the most widely used benchmark, but recent research suggests some nuance. Morningstar's December 2025 analysis recommends 3.9% as the safe starting withdrawal rate for new retirees — up from 3.7% in 2024 due to improved bond yields. Meanwhile, Bill Bengen himself (the rule's creator) now suggests that 4.7% may be safe with portfolios that include small-cap value stocks.
For early retirees planning 40-50+ year retirements (typical in the FIRE community), a more conservative 3-3.5% withdrawal rate is generally recommended. This means using a Rule of 28-33 instead of Rule of 25. Our FIRE calculator lets you adjust the withdrawal rate from 3% to 5% so you can model different scenarios.
Types of FIRE
Not everyone pursuing FIRE has the same target lifestyle. The FIRE community recognises several flavours, each with different expense levels and corresponding FIRE numbers:
| FIRE type | Annual expenses | FIRE number (at 4%) | Lifestyle |
|---|---|---|---|
| Lean FIRE | Under $40,000 | Under $1,000,000 | Minimal — housing, food, basics. No frills. |
| Regular FIRE | $40,000 – $80,000 | $1M – $2M | Comfortable with travel, dining, hobbies. |
| Fat FIRE | $100,000+ | $2,500,000+ | Generous lifestyle, no financial constraints. |
| Barista FIRE | Varies | Partial | Semi-retired with part-time work covering some costs. |
Lean FIRE is the most achievable numerically but requires a frugal lifestyle indefinitely. It works well for people in lower cost-of-living areas or countries. The risk is that there is little margin for unexpected expenses.
Regular FIRE is the sweet spot for most people — enough to live comfortably with travel, eating out, and hobbies, but not extravagantly. This is what most FIRE calculators target.
Fat FIRE requires substantially more savings but allows a generous retirement lifestyle. It is typical for higher-income professionals who do not want to significantly change their spending habits in retirement.
Barista FIRE is a pragmatic middle ground: you accumulate enough investments to cover most of your expenses, then work a relaxed part-time job (barista, freelance, seasonal work) to fill the gap and maintain health insurance. This dramatically reduces the savings target and provides social structure.
Why your savings rate matters more than your income
The single most important variable in reaching FIRE is not how much you earn — it is what percentage of your income you save and invest. This is because a higher savings rate has a double effect: it increases how much you invest each year AND it proves you can live on less, which lowers your FIRE number.
| Savings rate | Approximate years to FIRE |
|---|---|
| 10% | ~40 years |
| 20% | ~30 years |
| 30% | ~24 years |
| 40% | ~19 years |
| 50% | ~17 years |
| 60% | ~12 years |
| 70% | ~8.5 years |
| 80% | ~5.5 years |
These figures assume a 7% real (inflation-adjusted) return and starting from zero savings. The relationship is not linear — going from 10% to 20% savings cuts 10 years off the timeline, while going from 70% to 80% only cuts 3 years. The biggest gains come from increasing a low savings rate.
A complete FIRE example
Let us walk through a detailed example. Meet Alex, age 30, who earns $85,000 after tax and currently has $40,000 in investments.
Step 1: Calculate annual expenses. Alex tracks spending and finds they spend $50,000 per year on everything — rent, food, transport, entertainment, insurance, and miscellaneous expenses.
Step 2: Calculate the FIRE number. $50,000 × 25 = $1,250,000. This is Alex's FIRE number at a 4% withdrawal rate.
Step 3: Calculate annual savings. Alex earns $85,000 and spends $50,000, so they save $35,000 per year. That is a 41% savings rate.
Step 4: Project the timeline. Starting with $40,000 invested, adding $35,000 per year, and assuming a 7% real return:
| Year | Age | Portfolio value | % of FIRE number |
|---|---|---|---|
| Now | 30 | $40,000 | 3.2% |
| Year 5 | 35 | $259,000 | 20.7% |
| Year 10 | 40 | $548,000 | 43.8% |
| Year 15 | 45 | $934,000 | 74.7% |
| Year 18 | 48 | $1,260,000 | 100.8% |
Result: Alex can reach financial independence at age 48 — about 18 years from now. Notice how the portfolio growth accelerates in the later years as compound interest takes effect. The first $500,000 takes about 10 years; the second $500,000 takes only about 6 years.
The power of reducing expenses
Every dollar you cut from your annual expenses reduces your FIRE number by $25 (at a 4% withdrawal rate). This is one of the most powerful levers in FIRE planning.
If Alex reduces annual expenses from $50,000 to $45,000 (a $5,000 reduction), the FIRE number drops from $1,250,000 to $1,125,000 — a $125,000 reduction in the savings target. Plus, Alex now saves $40,000 per year instead of $35,000. The combined effect cuts roughly 3 years off the timeline.
Common areas where FIRE seekers cut expenses include housing (downsizing, house hacking, relocating), transportation (one car instead of two, cycling), food (cooking at home, meal planning), and subscriptions and lifestyle inflation.
Country-specific FIRE considerations
New Zealand
KiwiSaver is locked until age 65, so NZ early retirees need a "bridge strategy" — enough in taxable investment accounts to cover expenses from retirement until age 65, when KiwiSaver and NZ Super (approximately $24,000/year for a single person) kick in. NZ has no capital gains tax on shares held long-term, making it particularly favourable for FIRE investing.
Australia
Superannuation is locked until preservation age (60 for most). Like NZ, Australians need taxable investments to bridge the gap. The Age Pension provides about A$28,000/year for singles. Australia's franking credits on dividends are a significant advantage for FIRE investors using Australian shares.
United States
The Roth IRA conversion ladder is a key US FIRE strategy — it allows tax-free access to retirement funds before age 59½ by converting Traditional IRA funds to Roth and waiting 5 years. Social Security provides a baseline income from age 62 (reduced) or 67 (full). The 401(k) and IRA contribution limits are generous at $23,000 and $7,000 respectively.
United Kingdom
The UK State Pension (currently about £11,500/year) is available from age 66, rising to 67. ISAs allow tax-free growth with a £20,000 annual contribution limit — a powerful vehicle for FIRE savings. SIPPs (Self-Invested Personal Pensions) are accessible from age 55 (rising to 57 in 2028).
Canada
The TFSA (Tax-Free Savings Account) allows tax-free investment growth with a current cumulative limit of over $95,000. RRSPs provide pre-tax savings but are taxed on withdrawal. CPP/OAS provide baseline retirement income from age 65. Canada has no capital gains tax on primary residences.
Common FIRE mistakes to avoid
Ignoring inflation. A million dollars today will not buy a million dollars worth of goods in 20 years. Always use real (inflation-adjusted) returns when projecting your FIRE timeline. At 3% inflation, your expenses will roughly double over 24 years.
Forgetting healthcare costs. If you retire before you are eligible for public healthcare or employer-provided insurance, private health insurance can be a significant expense. Factor this into your annual expense estimate.
Underestimating expenses. Track your actual spending for at least 6-12 months before setting your FIRE number. Many people underestimate what they spend by 20-30%. Include irregular expenses like car replacement, home maintenance, and travel.
Being too aggressive with withdrawal rate. A 4% withdrawal rate has strong historical support for 30-year retirements. But if you are retiring at 35 and need 50+ years of income, consider using 3-3.5% for extra safety — or plan for some flexibility in your spending during market downturns.
Neglecting to enjoy the journey. FIRE is a marathon, not a sprint. Extreme deprivation for 10 years is not sustainable for most people. Find a savings rate that is aggressive but allows you to enjoy your life today. The perfect is the enemy of the good.
How to accelerate your FIRE timeline
Increase your savings rate by 5%. Even a small increase compounds dramatically over time. Going from 20% to 25% can cut 4-5 years off your timeline.
Invest in low-cost index funds. The difference between a 0.1% expense ratio index fund and a 1.5% actively managed fund costs hundreds of thousands of dollars over a FIRE timeline. Total market or S&P 500 index funds from providers like Vanguard, Fidelity, or local equivalents are the standard FIRE investment.
Maximise tax-advantaged accounts first. KiwiSaver (NZ), 401k/IRA (US), Super (AU), RRSP/TFSA (CA), ISA/SIPP (UK). These reduce your tax burden and accelerate compounding.
Consider geographic arbitrage. Retiring in a lower cost-of-living country or region can dramatically reduce your FIRE number. Moving from Auckland to a provincial NZ town, or from London to Portugal, can cut expenses by 30-50%.
Build multiple income streams. Side income from freelancing, rental property, or online business accelerates savings while also providing backup income in early retirement.