Methodology

One unit: today's dollars

All amounts are in today's dollars, so the return used in every calculation is the return after inflation (real). When you enter a return before inflation (nominal), it is converted with the exact Fisher formula, not by subtracting:

Real return = (1 + nominal) ÷ (1 + inflation) − 1

For example, 7% with 3% inflation is 3.88%. Your yearly saving is assumed to rise with inflation, so it is constant in today's dollars.

Formulas

FIRE number

F = annual spending ÷ withdrawal rate

At 4%, F is 25 times your annual spending. Lean and fat FIRE use the same formula with a different budget.

Portfolio after t years

P(t) = P × (1 + r)^t + S × ((1 + r)^t − 1) ÷ r

P is what you have invested now, S your saving per year, added at the end of each year, and r the real return. With r = 0 it is P + S × t.

Years to financial independence

n = ln((F × r + S) ÷ (P × r + S)) ÷ ln(1 + r)

This solves P(n) = F. Results are given to one decimal; between year ends the formula interpolates, so round up if you invest once a year. If the portfolio never reaches F (for example with a negative return), the calculator says so.

Coast FIRE number

Coast = F ÷ (1 + r)^N

N is the number of years until your retirement age. It is the amount that reaches F at that age with no more saving.

Years to coast FIRE

t = −ln(1 − r × (Coast − P) ÷ S) ÷ ln(1 + r)

This is when your portfolio, still growing with your savings, meets the coast number for that age: from then on it reaches F at your retirement age without more saving.

Net worth percentile

The net worth calculator uses the Federal Reserve's 2025 Survey of Consumer Finances public data. For each age group of the head of the family we compute the 1st to 99th weighted percentiles, pooling the survey's five imputations, and place your net worth between the two nearest by linear interpolation. Our medians match the Federal Reserve's official ones within 0.2%. Medians and averages for 2022 and 2025 are the Federal Reserve's own figures, in 2025 dollars.

Default assumptions

The calculators open with an example. Every value can be changed, and none of them is a forecast or a recommendation.

What the calculators leave out

• Taxes and investment fees.
• Social Security, pensions and other income in retirement.
• The order of returns: every year has the same return, while real markets vary and a bad start to retirement matters most.
• Healthcare costs before Medicare, and any large one-off expense.

How the calculators are tested

The same code runs in your browser and builds the numbers in the text of each page, so the two never disagree. Before every update an automated test suite checks it, and if a test fails the update is not published. Among the checks:

• $40,000 a year at 4% gives a FIRE number of $1,000,000, and $25,000 gives $625,000.
• $1,000,000 in 30 years at 5% real needs $231,377 today.
• 7% before inflation with 3% inflation is 3.88% real.
• Saving $100,000 a year from zero at 5% real reaches $1,000,000 in 8.3 years; saving $10,000 takes 36.7 years.
• The portfolio at the year given as the answer equals the goal, and coast FIRE dates reach the goal exactly at retirement age.
• Edge cases: a zero or negative return, no savings, a goal already reached and a 0% withdrawal rate.

Privacy of your numbers

The calculations run in your browser. Nothing you type is sent to Enough Path. The share link keeps the scenario after the "#" in the address, which browsers do not send to the server, and visit statistics are recorded without it.

Change log

• October 17, 2026: first version, with the FIRE calculator and the coast FIRE calculator.
• October 18, 2026: net worth by age calculator with the Federal Reserve's 2025 Survey of Consumer Finances.