Monte Carlo retirement calculator
Guide · By Kevin Lan · Updated September 2026
A Monte Carlo retirement calculator runs your plan across hundreds of possible market paths and reports the probability your money lasts — a chance of success, not a single straight-line guess.
What Monte Carlo adds
A Monte Carlo simulation runs your retirement plan across hundreds of randomized market sequences and counts how often the money survives. The result is a success rate — say 90% — instead of one straight line. A plain projection assumes a single steady return every year; real markets deliver good and bad years in an order you can't predict, and that order matters.
Why the order of returns matters
The same average return can end very differently depending on when the bad years land. A steep loss early in retirement, while you're also withdrawing, can permanently shrink the portfolio — this is sequence-of-returns risk. A fixed-return calculator can't see it; Monte Carlo does, because it tries thousands of orderings and reports how many leave you solvent.
How to read the result
A success rate of roughly 85–95% is commonly treated as comfortable. A perfect 100% often means you're over-saving and could retire sooner or spend more; well below about 75% suggests trimming spending, saving more, or working a little longer. It's a probability from historical-style assumptions — a stress test, not a promise.
Run it on your own plan
The calculator below finds your FIRE number and the year you reach it for free. The iPhone app adds the Monte Carlo chance-of-success simulation so you can pressure-test that date across many market paths, not just one.
FIRE calculator
Runs in your browser — nothing is sent anywhere.
Frequently asked questions
What is a Monte Carlo retirement simulation?
It's a method that runs your plan across hundreds or thousands of randomized market return sequences and reports the share in which your money lasts the whole retirement — a probability of success rather than a single projection.
What is a good Monte Carlo success rate?
Around 85–95% is widely considered comfortable. A 100% result may mean you're over-saving; below roughly 75% suggests lowering spending, saving more, or delaying retirement.
Is Monte Carlo better than the 4% rule?
They answer different questions. The 4% rule is a quick benchmark for how much you need; Monte Carlo stress-tests a specific plan against many market paths. Using both — the rule to size the target, a simulation to check it — is stronger than either alone.
Related guides
Find your date, then count down to it
See your number free above, then put the countdown on your iPhone home screen.