FatFIRE Math

Calculator

Calculate your Fat FIRE number and a historical time range.

Annual spending and the withdrawal rate set the target. Current savings and annual contributions are then replayed from each available starting year to show how long the target took to reach under past returns.

Your numbers

Today's dollars. Inputs stay in this browser.

What the Fat FIRE life costs each year, in dollars.
Percent of the portfolio taken in the first year. 4% is the classic; long Fat FIRE retirements often use less.
Retirement accounts and taxable investments. Leave out your home.
Percent a year above inflation — raises, minus lifestyle creep.
Allocation
Stocks with a fifth in 10-year Treasuries — the usual Fat FIRE accumulation mix.
Presets: Seattle software developer · Cincinnati plumber · Texas doctor
Your Fat FIRE number $5,714,286 The portfolio that supports the spending at that rate.
Median time to get there 21 years Half of all starting years were faster than this.
Fastest start on record 14 years The shortest accumulation period in the record.
Slowest start on record 30 years The longest accumulation period that reached the target.

On the median starting year, this plan reached $5,714,286 in 21 years. Across the 78 starting years the record can judge, the quickest took 14 and the slowest took 30. Every one of them got there inside the time you gave the plan.

Exhibit 1 — the climb, from every starting year Real dollars, 1928–2024
Every starting year on record, climbing towards your Fat FIRE number$0$2.0M$4.0M$6.0MYour number, $5.7MNow+10+20+30+40
One faint line per starting year, each stopping the moment it clears your number. The green line is the median start. Lines in rust never got there inside the time you gave the plan.
Exhibit 2 — how long it took, by starting year Taller is slower
Years taken to reach the number, by the year the saving started0y10y20y30y40y1940196019802000
Each bar is the number of years the same plan took to reach its target from that historical starting year.
Which start Began Time taken Arrived
Fastest start on recordThe shortest historical accumulation period. 1985 14 years 1999
The median startHalf of all starting years were quicker than this. 1932 21 years 1953
Slowest start that still got thereThe longest historical accumulation period that reached the target. 1956 30 years 1986
Started in 1929Starting the month before the crash. 1929 24 years 1953
Started in 1966Into the long inflation years. 1966 24 years 1990
Started in 1973The oil shock and a 45% real drawdown. 1973 20 years 1993
Started in 1999Straight into the dot-com bust. 1999 22 years 2021

Pre-tax and before fees, in today's dollars. The withdrawal rate is applied to the portfolio at retirement and raised with inflation after that — see about and method for exactly what runs underneath, or test the retirement itself once you have a number.

How to read the range

The median describes the middle historical starting year. Exhibit 2 also shows the faster and slower results, including starts that did not reach the target within the selected horizon. If the slow version still lands before you want to stop working, the plan holds.

What Fat FIRE costs → Where the 4% rule stops working →