How this FIRE calculator works
Enter what you spend in a year, the share of your take-home pay you save, your current invested net worth and an expected return after inflation. The calculator works out your implied income and annual savings, then grows your net worth month by month.
Your FIRE number is your annual expenses divided by your safe withdrawal rate — 25 times expenses at the default 4%. The calculator also shows Lean FIRE, based on 75% of your current spending, and Fat FIRE, based on 150%, so you can see the range from a frugal to a comfortable early retirement.
For each target it reports how long until your projected net worth reaches it. Turn on Compare to see how a higher savings rate changes your timeline.
The FIRE math
FIRE planning combines the withdrawal-rate rule with steady compound growth:
FIRE number = annual expenses ÷ withdrawal rate Income = expenses ÷ (1 − savings rate)
- Annual savings = income − expenses
- Each month: net worth = net worth × (1 + i) + savings ÷ 12
- i = monthly real return
- Lean = 0.75 × expenses ÷ rate; Fat = 1.5 × expenses ÷ rate
Worked example
Someone spending $45,000 a year who saves 30% of take-home pay has an implied income of about $64,300 and saves about $19,300 a year. Their Regular FIRE number is $1,125,000. Starting with $75,000 invested and a 5% real return, they reach it in roughly 24 years.
Raise the savings rate to 50% — the same spending, but a higher income or a leaner budget — and annual savings jump to $45,000, cutting the timeline to just under 15 years. Lean FIRE at about $844,000 arrives several years earlier; Fat FIRE at about $1.69 million takes longer.
What FIRE means
FIRE stands for Financial Independence, Retire Early. Financial independence is the point where your investments can cover your living costs indefinitely, so work becomes optional. Many people in the FIRE community keep working in some form; the goal is choice, not necessarily idleness.
The core idea is simple: spend well below what you earn, invest the difference in low-cost diversified funds, and let compounding do the rest. The math shows why your savings rate, more than your investment returns, decides how fast you get there.
Why savings rate matters most
Your savings rate works twice. A higher rate means more money invested each year, and it also means lower spending, which lowers the FIRE number you need. That's why moving from a 20% to a 50% savings rate can cut decades from your timeline, while squeezing an extra percentage point of return makes a smaller difference.
Small permanent changes compound too. Housing, transportation and food are usually the biggest levers; recurring subscriptions and insurance re-shopping add up as well.
Lean, Regular and Fat FIRE
Lean FIRE means financial independence on a minimal budget, which makes the target smaller but leaves little room for surprises. Regular FIRE covers your current lifestyle. Fat FIRE funds a more generous lifestyle with extra margin for travel, family support or higher health costs.
There are no official definitions. ClearCalc uses 75% of your current spending for Lean and 150% for Fat so the three numbers are easy to compare. Adjust your expenses input to model your own idea of each.
Choosing a withdrawal rate
The 4% rule was studied for 30-year retirements. If you retire at 40, your money may need to last 50 years or more, so many early retirees plan around 3.25% to 3.5%. That raises your FIRE number from 25 times expenses to roughly 29 to 31 times. Flexibility helps: being willing to cut spending in bad market years, or earning some part-time income, makes a higher rate safer.
Costs early retirees often underestimate
In the US, health insurance before Medicare eligibility at 65 is a major expense; marketplace plans, subsidies and health savings accounts all affect your budget. Retirement accounts generally charge a 10% penalty on withdrawals before age 59½, though strategies such as Roth contribution withdrawals, Roth conversion ladders and certain exceptions can provide access. Taxes on withdrawals, home repairs and supporting family also belong in your spending estimate.
Build a cushion: many people aim slightly above their number, keep a cash reserve for one or two years of spending, or plan a phased retirement with some earned income.
Frequently asked questions
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Open calculatorNot financial advice. ClearCalc provides estimates for educational purposes only. Results depend on the assumptions you enter and may differ from offers from lenders or institutions. Consult a qualified professional before making financial decisions.