Risk of ruin calculator
Risk of ruin is the chance that a run of losses takes an account down to a level it does not recover from. This calculator simulates your record forward at the size you trade and gives the chance of a 50% drawdown within 500 trades, the longest losing run to expect, and the largest risk per trade that survives that run.
Last updated 30 September 2026.
Within the next 500 trades, at the size you entered, if your measured win rate is your real one.
The largest risk per trade that keeps a run that long inside a 50% drawdown.
300 simulated accounts, each risking a fixed share of its current balance. A system with no edge reaches ruin at any size given long enough; smaller risk only makes it take longer.
What moves the result
- Risk per trade moves it most. Halving the size does far more than a slightly better win rate.
- Win rate and reward to risk together decide whether there is an edge at all. Without one, ruin is a matter of time at any size.
- The number of trades matters because a long record contains longer losing runs than a short one.
Why the losing run is the thing to size for
An edge does not protect an account from a run of losses; it only makes the run rarer. The calculator estimates the longest run your win rate will produce over a few hundred trades and works back to the size that keeps that run survivable. If the size you trade is above it, the account is relying on the run not arriving.
What it leaves out
It assumes your measured win rate is your real one, which a small record cannot confirm, and that trades are independent. It also assumes you keep trading the same size through the drawdown, which is the hard part.
A calculator shows what follows from the numbers you enter. It is not a forecast and not personal financial advice. Trading carries risk and you can lose money.
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