FIRE — Financial Independence, Retire Early — describes a movement built around aggressive saving and investing with the goal of reaching financial independence, and often stopping traditional full-time work, well before conventional retirement age. Stripped of the lifestyle branding, it's built on a small set of straightforward financial principles.
The core math: the safe withdrawal rate
The central idea is a target multiple of annual expenses — commonly 25 times annual spending — based on a commonly cited starting point of a roughly 4% annual withdrawal rate that has a historical track record of lasting several decades in typical market conditions. Reaching 25 times your annual expenses in invested assets is considered, under that framework, enough to sustain indefinite withdrawals without depleting the principal in most historical scenarios.
Why the savings rate matters more than the salary
FIRE math emphasizes savings rate — the percentage of income saved and invested — over income level alone, because savings rate determines both how fast the target is reached and how large the target needs to be (a lower spending level means a smaller required multiple). Someone saving 50% of income can reach financial independence dramatically faster than someone saving 10%, even at a lower income, since both the target and the funding speed move in their favor.
Honest trade-offs and risks
The safe withdrawal rate is based on historical data, not a guarantee — sequence-of-returns risk (a market downturn early in retirement) can meaningfully affect outcomes, and many FIRE planners now discuss more conservative withdrawal rates or flexible spending as a buffer. Retiring earlier also means a longer time horizon for the money to last, generally warranting more caution than the standard 4% figure, which was originally studied around a 30-year retirement period.
There's also a personal dimension often underweighted in the math: leaving full-time work earlier has real implications for healthcare access, social structure, and purpose that vary enormously by individual and country, and are worth thinking through as seriously as the financial calculation itself.
Modeling your own FIRE number
Estimate your annual spending, multiply by 25 as a starting target (adjusting for a longer-than-30-year horizon if retiring very early), then use our retirement calculator with your current savings, contribution rate, and expected return to project when you'd reach that target. Layer in our inflation calculator to express the target in future money rather than today's prices, since the number needs to hold its value over a potentially very long retirement.