How to calculate your FIRE number

The simplest formula

The most common starting point is the 4% rule:

FIRE number = Annual spending in retirement × 25

Why 25? Because 1 ÷ 0.04 = 25. If you withdraw 4% of your portfolio in year 1, and adjust for inflation after, historical data suggests the portfolio often lasted 30 years for a balanced (60/40) portfolio.

Example: if you expect to spend ₹12 lakh per year in retirement, your rough FIRE number is ₹12 lakh × 25 = ₹3 crore.

Step 1: Estimate retirement spending

Don’t use your current gross income. Use your expected spending in retirement.

Category	Estimate (₹/year)	Notes
Housing	…	Rent vs fully paid home? EMIs end? Property tax? Maintenance?
Food & groceries	…	Often drops slightly, but not dramatically.
Utilities & transport	…	May fall if not commuting daily.
Healthcare	…	Tends to rise with age. Budget generously.
Insurance	…	Health, term, home — what remains?
Discretionary	…	Travel, hobbies, gifts — be realistic.
Taxes	…	Depends on account types (taxable vs tax-deferred), location, capital gains.
Buffer	…	Unexpected expenses (car, home repair).

Pro tip: Track actual spending for 3–6 months. Many people find they’re spending 20–30% less than they think, but healthcare is often underestimated.

Step 2: Choose a safe withdrawal rate (SWR)

The “×25” assumes a 4% initial withdrawal, inflation-adjusted thereafter. But that’s not universal.

SWR	Multiple	When to use
4.0%	25×	Reasonable starting point for many 30-year horizons with a balanced portfolio.
3.75%	~26.7×	A bit more conservative if you want extra margin.
3.5%	~28.6×	Safer for longer horizons (35–40 years), high equity valuations, or low bond yields.
3.33%	30×	Very conservative; common for “Fat FIRE” or those wanting high confidence.
4.5%	~22.2×	Only reasonable with high flexibility (cut spending in bad years), shorter horizon, or very conservative asset mix? Historically rare to sustain.

Post-2020, many researchers argue 3.5–3.75% is more prudent than 4% given lower expected real bond yields. Morningstar’s annual “State of Retirement Income” often lands around 3.7–4.0% depending on assumptions.

Step 3: Account for other income

Your FIRE number doesn’t need to cover spending that’s already guaranteed.

Subtract reliable income:

• Pension (government/private) — only count if inflation-adjusted and likely to continue.
• Annuity income — guaranteed portion.
• Rental income — be conservative (vacancy, maintenance, taxes).
• Social security / state pension — count realistically, not optimistically.

Adjusted FIRE number = (Annual spending – Reliable income) × SWR multiple

Example: spending ₹12 lakh, pension ₹4 lakh/year (reliable) → need to cover ₹8 lakh. At 4% (25×), that’s ₹2 crore instead of ₹3 crore.

Step 4: Stress-test your number

A single multiple is a starting point. Stress-test with these checks:

Check	Why
Monte Carlo	See probability of success across thousands of paths, not just history. Try our Monte Carlo simulator.
Bad-early sequence	Test a 1966–1975 style start (high inflation + poor returns early). See Sequence of returns.
Longer horizon	If retiring at 45, plan for 45–50 years, not 30. Consider 3.3–3.7% SWR.
Higher healthcare	Add ₹1–2 lakh/year from age 70–75 onward as a sensitivity.
Inflation shock	Stagflation (high inflation + flat markets) is brutal. Ensure your plan survives it.
Tax drag	Model withdrawals from taxable accounts (capital gains) vs tax-deferred. Tax location matters.

Step 5: Build in buffers

• Emergency fund separate from FIRE portfolio. 6–12 months of spending outside your retirement stash.
• Sequence buffer (cash). 1–2 years in cash reduces forced selling. See Bucket strategy.
• Flexibility. “If markets are down, I’ll cut discretionary by 15%” is often more powerful than saving an extra ₹20 lakh.
• Barista option. Part-time work earning ₹2–5 lakh/year can dramatically cut your required stash.
• Geographic arbitrage. Moving to a lower-cost location later is a valid plan B.

A complete worked example

Profile: 35, wants to retire at 55 (20-year horizon). Plans to spend ₹10 lakh/year in retirement.

1. Baseline: ₹10 lakh × 25 = ₹2.5 crore (4% SWR, 30-year horizon assumption). But horizon is 20 years now? Actually at 55, likely 30–35 more years.
2. Conservative SWR: use 3.5% (28.6×) → ₹2.86 crore.
3. Account for state pension: expects ₹3 lakh/year at 60 (count conservatively) → need to cover ₹7 lakh for first 5 years (55–60), then ₹4 lakh after. Approximate net → target closer to ₹2.2–2.4 crore.
4. Stress-test: Monte Carlo at 2.4 crore gives ~85–90% success with 60/40; bad-early sequence is tight. Add 1-year cash buffer + spending flexibility → comfortable.
5. Final target: ₹2.4–2.6 crore range, depending on conservatism.

Common mistakes to avoid

• Using current income. “I earn ₹30 lakh” doesn’t mean you’ll spend ₹30 lakh in retirement. Track spending.
• Ignoring healthcare costs. This is the #1 under-estimate. Get realistic numbers for your country.
• Forgetting taxes. ₹3 crore in PF/NPS is not the same as ₹3 crore in a taxable account.
• Using nominal returns. If you calculate in nominal and spend in real, you’ll be off. Prefer real returns throughout.
• Chasing a precise number. FIRE is directional. A range (₹2.4–2.7 crore) is far more honest than ₹2,487,500.
• Assuming you’ll never adjust. The original Trinity study showed many failures were avoided by small spending cuts. Build flexibility in.
• Ignoring sequence risk at the start. A bad first 5 years breaks many plans; protect them.
• Lifestyle inflation. As you get closer, it’s easy to inflate your “retirement spending” number.

Quick sanity checks

• Multiply by 20: If your target feels impossibly large, check if you’re using 25× on gross income. Use spending.
• Coast check: See if you’re already Coast FIRE via Coast FIRE calculator.
• Can you live on less? Try a “Lean FIRE” number (e.g. ₹7–8 lakh spending) to see how much easier it becomes.
• Run probability: Don’t just ask “will it work?” — ask “how likely?” with Monte Carlo.

Bottom line

Start with annual spending × 25. Then subtract guaranteed income. Then stress-test with a more conservative multiple (28–30×) or Monte Carlo. Finally, add buffers and flexibility. The goal isn’t perfection — it’s a robust plan you can actually stick to.