What's your FIRE number?

Most FIRE calculators use a simple formula: 25× expenses, then apply a flat real return. This one runs a month-by-month simulation — it compounds your portfolio at nominal returns each month, adds your SIP, steps it up every year (like a salary hike would), then converts to today's rupees at each checkpoint. This means inflation is handled precisely via month-by-month compounding, not a rough subtraction. The difference can be 2–4 years in your FIRE timeline.

A 10% annual SIP step-up means you increase your monthly investment by 10% every year — roughly matching a salary increment. Most calculators ignore this. The impact is enormous: a ₹25,000 SIP with 10% annual step-up produces nearly the same corpus in 20 years as a flat ₹60,000 SIP. It's the single biggest lever most people underestimate.

It's the inverse of the 4% safe withdrawal rate. The Trinity Study found that withdrawing 4% of a portfolio annually (adjusted for inflation) has a ~95% probability of lasting 30+ years across historical market cycles. 1 ÷ 0.04 = 25. So 25× annual expenses = a corpus that sustains you indefinitely at your current lifestyle.

Today's rupees — specifically, today's purchasing power. We project your portfolio in nominal terms (actual future rupees) and divide by cumulative inflation at each year to get the real value. So when we say "FIRE at 47," we mean your portfolio at 47 will buy what 25× your current expenses buys today. Inflation is baked in, not ignored.

Nifty 50 and Sensex have historically delivered 12–14% CAGR over 20+ year periods. For a diversified equity mutual fund portfolio, 12% pre-tax is a reasonable long-term assumption. Use 10–11% if you want to be conservative or include some debt. Post-FIRE, you'd typically reduce equity exposure, but the calculator uses the same rate for simplicity — adjust as needed.