About the FIRE Number Calculator
Financial Independence, Retire Early (FIRE) has one core number behind it - the portfolio size that lets you withdraw enough to cover expenses indefinitely, typically using the 4% rule. Our FIRE Number Calculator finds that target and projects how long it takes to reach it.
How It Works
The calculator divides your annual expenses by your chosen withdrawal rate (commonly 4%, based on historical safe-withdrawal-rate research) to find your FIRE number - the portfolio size that theoretically supports your expenses indefinitely. It then projects your current savings and monthly investments forward to estimate how many years until you reach that number.
Formula & Methodology
The 4% rule comes from historical research (the 'Trinity Study' and related analyses) into how a diversified stock-and-bond portfolio would have performed across rolling 30-year historical periods if a retiree withdrew a fixed percentage annually, adjusted for inflation. Dividing expenses by the withdrawal rate is mathematically the same as multiplying expenses by 25 (since 1 ÷ 0.04 = 25), which is why '25 times annual expenses' is the shorthand version of the same 4% rule target.
Step-by-Step: Calculating It By Hand
- 1Total your annual expenses (or projected retirement expenses).
- 2Choose a withdrawal rate - 4% is the traditional starting point, though some choose a more conservative 3-3.5% for extra safety margin.
- 3Divide annual expenses by the withdrawal rate (as a decimal) to find your FIRE number.
- 4Project your current savings and contributions forward to estimate years remaining until reaching that number.
Examples
Standard 4% rule
$50,000 in annual expenses at a 4% withdrawal rate means a FIRE number of $1,250,000 - the portfolio size theoretically supporting that spending indefinitely.
More conservative withdrawal rate
The same $50,000 in expenses at a more conservative 3.5% withdrawal rate raises the FIRE number to about $1,428,571 - a meaningfully higher target for extra safety margin.
Advantages
- Uses the well-established 4% rule framework, adjustable to a more conservative rate if desired
- Projects a realistic years-to-FIRE timeline based on current savings and contribution rate
- Makes an ambitious goal concrete with a specific dollar target and timeline
- Useful for testing how increasing savings rate accelerates the timeline
Common Mistakes
- Treating the 4% rule as a guarantee rather than a historically-based guideline with real sequence-of-returns risk
- Not adjusting the withdrawal rate lower for a longer retirement horizon (retiring at 35 needs more safety margin than retiring at 65)
- Underestimating future expenses, especially healthcare costs before Medicare eligibility
- Assuming a constant investment return every year rather than realistic market volatility
Edge Cases to Watch For
- The 4% rule was derived from a roughly 30-year retirement horizon - someone retiring in their 30s or 40s faces a much longer retirement and often chooses a lower, more conservative withdrawal rate.
- Sequence-of-returns risk means poor market performance in the first few years of retirement can be far more damaging than the same poor performance later, something a flat withdrawal-rate rule doesn't directly address.
- Healthcare costs before Medicare eligibility (age 65) are a major, often underestimated expense category for early retirees to budget into their annual expenses figure.
- A 'Coast FIRE' or 'Barista FIRE' variant targets a lower number that grows to full FIRE with time alone, or is supplemented by part-time income, rather than needing to hit the full FIRE number before any spending begins.
Common Use Cases
- Calculating a target portfolio size for financial independence
- Projecting a timeline to reach FIRE based on current savings and contributions
- Testing how increasing monthly investments accelerates the timeline
- Understanding how withdrawal rate assumptions change the required portfolio size