Your savings rate matters more than your income
The defining insight of the FIRE movement is that time to financial independence depends almost entirely on the percentage of income you save — not on how much you earn.
The reason is that your savings rate works from both ends simultaneously. Saving more builds the portfolio faster, and spending less shrinks the target you are building toward. Someone earning $90,000 and spending $54,000 saves 40% and reaches independence in roughly 17 years. Someone earning $200,000 but spending $160,000 saves 20% and takes far longer, despite a much larger income.
This is why income alone predicts financial independence poorly. High earners who scale spending with income can work indefinitely, while moderate earners with disciplined spending reach independence remarkably early.
Where the 25× number comes from
Your FIRE number is your annual spending multiplied by 25, which is simply the inverse of a 4% withdrawal rate. Spending $54,000 a year gives a target of $1,350,000.
The 4% figure comes from the Trinity Study and William Bengen's research on historical US market data, which found it survived every rolling 30-year period tested — including retiring immediately before the 1929 crash.
The important caveat for early retirees: that research assumed a 30-year retirement. Retiring at 40 may mean funding 50 years, and the safe rate falls as the horizon extends. Most careful early retirees use 3% to 3.5%, which raises the target to 28–33× spending. That is a meaningful difference — at 3.5%, the same $54,000 of spending needs about $1,543,000 rather than $1,350,000.
The variants worth knowing
Lean FIRE means reaching independence on a deliberately minimal budget. It gets you there years sooner but leaves little margin — a major medical event or a sustained bear market has fewer places to absorb.
Fat FIRE targets a comfortable rather than minimal retirement, typically 1.5× or more of current spending. It takes considerably longer but carries far more resilience.
Coast FIRE is the most practically useful for people early in their careers. It is the amount you need invested *today* such that, with no further contributions, compounding alone grows it to your FIRE number by traditional retirement age. Reaching Coast FIRE means you can stop saving aggressively and simply cover your expenses — which opens up lower-paying but more interesting work without jeopardising retirement.
Barista FIRE sits between: enough invested to cover most expenses, with part-time work covering the rest, often for health insurance.
What this projection does not handle
The calculator assumes a constant real return, which no market delivers. Real returns arrive as long stretches of good years punctuated by sharp declines. Two people with identical averages can get very different outcomes depending on when the bad years arrive relative to their retirement date.
Sequence-of-returns risk is the specific danger. Poor returns in the first five years of drawdown force selling depressed assets, permanently shrinking the base. Standard defences include holding one to three years of expenses in cash, staying flexible on spending early on, and being willing to earn some income in bad years.
Healthcare is the largest practical obstacle to early retirement in the US, since Medicare does not begin until 65. Marketplace coverage for a family can run well over $1,000 a month, and that has to be in your spending figure.
Finally, the calculator ignores Social Security, which will eventually supplement withdrawals and means the portfolio does not need to carry the full load forever. That makes the projection somewhat conservative for anyone retiring in their 50s.
Frequently asked questions
- What withdrawal rate should early retirees use?
- 3% to 3.5% is the common recommendation for retirements longer than 30 years, versus 4% for a standard timeline. Lower rates mean a larger target but substantially more resilience.
- Should I use gross or take-home income?
- Take-home, since that is what you can actually save from. Employer 401(k) contributions should be added to your saving figure even though they never reach your account.
- Does the FIRE number include my house?
- No. Your FIRE number covers invested assets that generate income. A primary residence does not produce cash flow, though owning it outright reduces your annual spending and therefore lowers the target.
- What about inflation?
- Enter your return net of inflation — around 7% nominal minus 3% inflation gives roughly 4–5% real. The default 7% is described as after-inflation, so the result is already in today's money.