FI, the 4% rule, and the path to early retirement
Financial independence is the point where your invested portfolio can cover your living costs on its own. The math is simpler than it sounds: pick a safe withdrawal rate, divide your annual spending by it, and that’s the portfolio you’re aiming for. From there it’s a race between how much you save and how fast your investments grow.
The FI number
FI number = annual expenses ÷ withdrawal rate
At a 4% withdrawal rate that’s 25× your annual spending. We grow your portfolio in real terms — using a real return of (1 + return) ÷ (1 + inflation) − 1 — so every figure stays in today’s money.
What makes this calculator different
- A real FI number. Derived straight from your withdrawal rate (4% → 25× expenses), not a vague "how much do I need" guess.
- Years to FI, driven by saving. The timeline responds to your contributions and your savings rate — the levers you actually control.
- The Coast FIRE number. See whether you can stop saving today and still drift to FI by a traditional retirement age.
- Everything in today’s money. Real returns mean the FI number and the chart are directly comparable to what you spend now.
Frequently asked questions
What is my FI number, and where does the 4% rule come from?+
Your FI (financial independence) number is the portfolio that can fund your spending more or less indefinitely. It’s your annual expenses divided by your safe withdrawal rate. At a 4% withdrawal rate that works out to 25× your annual spending — the famous "25× rule" — because 1 ÷ 0.04 = 25. The 4% figure comes from the Trinity study, which found that withdrawing 4% of a stock-and-bond portfolio in the first year (then adjusting for inflation) historically lasted at least 30 years. Choose a lower rate for a longer or more cautious retirement, or a higher one if you’re comfortable with more risk.
Why does my savings rate matter more than my income?+
Years-to-FI depends on the gap between what you earn and what you spend, not on the raw size of your paycheck. A high savings rate does double duty: it pours more into the portfolio and it lowers the FI number you’re aiming at (because you live on less). That’s why someone saving 50% of their income reaches FI far sooner than someone saving 10%, even at the same salary. It’s the single biggest lever you control — which is why this calculator surfaces it as a headline stat.
What is Coast FIRE?+
Coast FIRE is the point where you’ve invested enough that, with no further contributions, ordinary market growth alone will carry your portfolio to your full FI number by a traditional retirement age. Once you’ve "coasted" you still need to cover your living expenses, but you no longer have to save for retirement — every extra dollar saved just brings the date forward. This calculator shows your Coast FIRE number and flags when you’ve already crossed it.
Why does this calculator work in today’s dollars?+
Inflation steadily erodes what a dollar buys, so a $1,000,000 portfolio decades from now won’t spend like $1,000,000 does today. To keep the numbers meaningful we work in real (inflation-adjusted) terms, using a real return of (1 + nominal return) ÷ (1 + inflation) − 1. Your FI number, the balance on the chart, and the Coast FIRE figure are all expressed in today’s money, so you can compare them directly against your current spending.
What does it mean if FI is "unreachable"?+
It simply means that, with the savings, returns, and spending you entered, the portfolio doesn’t reach your FI number within a 100-year horizon. Usually the fix is one of a few levers: save more each year, trim your target expenses (which also lowers the FI number), assume a higher long-run return, or accept a higher withdrawal rate. Small changes to the savings rate often have an outsized effect on the timeline.
Disclaimer: This calculator is for educational purposes only. Investment returns, inflation, and safe withdrawal rates are uncertain and vary over time, and past results don’t guarantee future ones. It is not financial advice.