FIRE Number Calculator

What FIRE actually is

FIRE, or Financial Independence, Retire Early, is the idea that if you save enough of your income, at some point your investments can cover your living costs and paid work becomes optional. The core maths is uncomplicated: the framework saves a high share of income, invests it for long-term growth, and treats a pot of 25 times annual expenses as the point where paid work becomes optional. The complication is in the inputs. Small differences in savings rate or return assumption produce enormous differences in the timeline.

Years to financial independence by savings rate

This is the result most FIRE explanations build around. Assume a 5% real return, a 4% withdrawal rate, a 25x target and a starting pot of zero. Years to financial independence by savings rate:

10% saved → 51.4 years to FI
20% saved → 36.7 years
30% saved → 28.0 years
40% saved → 21.6 years
50% saved → 16.6 years
60% saved → 12.4 years
70% saved → 8.8 years

Starting from zero at a 10% savings rate, the figure is 51.4 years. At 50%, it is 16.6. The non-linearity is the point: moving from a 10% to a 50% savings rate cuts spending from 90% of income to 50%, a reduction of a little under half, and cuts the timeline by roughly two-thirds. The reason is that spending less both increases contributions and reduces the target, since the target is 25x a smaller number. Both effects compound. A different return assumption moves every row: at 7% real the same series runs 41.7, 30.7, 24.0, 19.0, 15.0, 11.4 and 8.3 years.

The four FIRE variants

These are community labels for spending levels rather than settings in the calculator. The Lean FIRE and Fat FIRE rows in the results use the calculator's own convention (half the entered expenses and double them), so they track whatever figure is entered rather than the fixed bands described here.

Lean FIRE: a target of around 20,000–25,000 annual spending, requiring a pot of 500k–625k. Feasible on a single income with deliberate frugality; requires accepting a modest lifestyle permanently.

Regular FIRE: 35,000–50,000 annual spending, 875k–1.25m pot. Closest to retirement as it is usually understood, reached well before conventional retirement age.

Fat FIRE: 75,000+ annual spending, 1.9m+ pot. Requires high earnings through the accumulation phase, which in practice means occupations that pay well during those years, combined with disciplined saving.

Coast FIRE: describes contributing heavily in the 20s and 30s until the pot is large enough to compound to the full target unaided. Contributions then stop and earnings cover current spending only. The trade-off is that the heavy contributions fall in the earliest earning years.

What a higher income actually changes

FIRE calculators focus on savings rate, and there is a mathematical reason for that: under the model in the table above, the timeline does not depend on income at all. Someone saving 30% of 40,000 and someone saving 30% of 60,000 both reach financial independence in 28.0 years, because raising income by half raises the annual contribution and the 25x target by half as well. The income cancels out of the equation entirely.

What a higher income changes is which savings rates are liveable. Saving 50% of 40,000 leaves 20,000 to live on; saving 50% of 80,000 leaves 40,000. The rate is what compresses the timeline, and a larger income makes a high rate survivable at a spending level a household can accept. The 10-to-15-year timelines associated with high earners correspond to savings rates between roughly 54% and 67% at a 5% real return: the driver is the rate, not the size of the contributions.

The problem with the 4% assumption

FIRE's 25x target relies on the 4% withdrawal rule from the Trinity Study. That is a 30-year planning horizon. A FIRE retiree at 40 needs the pot to last 50 years or more, not 30. Research since the original study suggests safe withdrawal rates for 50-year retirements drop to 3.3–3.5%. That turns 25x into 28.6x to 30.3x, since 1 divided by 0.035 is 28.57 and 1 divided by 0.033 is 30.30. The change is proportional, so it scales the target by the same factor at every spending level. Some FIRE planners work from 3.5% and 30x rather than the popularised 4% and 25x.

Sequence-of-returns risk hits early retirees hardest

The first 5–10 years of a 50-year retirement are the danger zone. A 30% market fall in year two matters more than the same fall in year twenty, because the pot has not had time to grow beyond its starting figure. Approaches to this include a cash buffer holding two to three years of expenses in liquid savings, and a bond tent that holds a higher fixed-income allocation early and shifts equity-heavy later. The calculator models a level withdrawal; it does not model the order in which returns arrive.

What FIRE calculators don't model

Health costs are the big one. Where publicly funded healthcare begins at a set age, or where cover is tied to employment, an early retiree can face a gap between leaving work and that cover starting, and private cover across that gap can be a substantial recurring expense. The size of the gap and what it costs vary widely by country. Life events such as divorce, children's education, parental care or health issues can push spending above the planned base. What the calculator produces is a baseline figure from the expenses entered; it holds spending flat and models no cushion above it.

The one-more-year problem

When you hit your FIRE number, you may not actually stop. FIRE communities describe this as one-more-year syndrome. The thought process, that working one more year makes the pot larger and the safety margin wider, is reasonable in the moment and self-perpetuating, because it is equally reasonable a year later. The calculator produces the number; whether the number gets acted on is a separate problem.