Plan for the range,
not the average.
FatFIRE Math tests one plan against every historical starting year. No smooth return assumptions, no account, and no forecast pretending to be a result.
Start with the question.
Find your number
Turn retirement spending into a target, then replay the saving path through market history.
Test a retirement year
Start in any historical year and follow withdrawals, inflation and allocation through time.
Compare the decisions
Measure working longer, withdrawal rates, bad decades, legacy goals and phased retirement.
Do the math with people doing it too.
Join the FatFIRE Math community and share a group chat with 10 other people or families.
See the annual membershipHistory is uneven.
The math should be too.
US large-cap stocks returned 6.7% a year after inflation across the full record. No retiree experienced that smooth average. These tools replay the individual calendar years instead.
How the data worksBegin with a life that looks familiar.
Each preset is an editable illustration, not a claim about every household in that profession or city.
Understand the result before acting on it.
All guidesWhat Fat FIRE costs
How annual spending and the withdrawal rate set the target, and why a larger target does not add years in a straight line.
6 minute readWhere the 4% rule stops working
The research behind 4%, the assumptions it uses, and what changes when retirement lasts forty-five years instead of thirty.
8 minute readWhy the first five years matter
Two retirements with similar average returns produced very different results because the bad years arrived in a different order.
7 minute read