Home › Tools › Risk of ruin calculator
Free · runs in your browser · no signup
Risk of ruin is the chance that a losing streak takes your bankroll down to a level you cannot come back from before your run of bets is over. Take a real 5-point edge — you think 55%, the price is 50¢ — over 200 bets. Staking the Kelly amount, 10% of the bankroll each time, halves the bankroll at some point in 37% of simulations; half Kelly cuts that to 8%, and double Kelly raises it to 78% while the median result falls to 0.97× the start.
2,000 simulated bankrolls, each staking the same share of its current balance on independent bets, before fees. The result is only as good as your probability: if your edge is smaller than you think, the real risk is higher.
The same 5-point edge (you think 55%, the price is 50¢) over 200 bets, 4,000 simulated bankrolls for each stake size:
| Stake per bet | Halves at some point | Median result | Finishes ahead |
|---|---|---|---|
| 2.5% quarter Kelly | 0% | 1.55× | 89% |
| 5% half Kelly | 8% | 2.12× | 86% |
| 10% full Kelly | 37% | 2.72× | 74% |
| 20% double Kelly | 78% | 0.97× | 48% |
| 30% triple Kelly | 94% | 0.04× | 21% |
Median result = the middle final bankroll as a multiple of the start. Betting more than the Kelly stake adds risk without adding long-run growth.
Each bet buys a contract at price c. A win pays 1/c − 1 per dollar staked and a loss costs the stake. Because every bet is a share of the current balance, the bankroll never reaches exactly zero, so ruin here means falling to a level you choose — half the starting bankroll by default. The Kelly stake, (q − c) / (1 − c), is the share that maximises long-run growth when your probability q is right; at around twice that, long-run growth drops to roughly zero. Size single bets with the Kelly calculator, check the edge with the expected value calculator, or read about the Kelly criterion in the glossary.
Put real prices into the calculator: every page below shows current odds, 24-hour moves and the market rules.
Sports odds · Politics odds · Crypto odds
Most traded right now:
The chance that a run of losses takes a bankroll down to a level you cannot or will not recover from — here, a chosen share of the starting bankroll — before your planned number of bets is over.
The Kelly stake, (q − c) / (1 − c), maximises long-run growth if your probability is right. Because estimates are uncertain, many traders stake half or a quarter of it: in the example above, half Kelly halves the bankroll in about 8% of simulations against 37% at full Kelly.
Losing streaks happen even when every bet has positive expected value. The larger each stake is relative to the bankroll, the more likely a streak cuts it down before the edge pays off.
🔔 Free Telegram watchlist of big odds moves
All tools · Polymarket fees · Polymarket vs Kalshi odds · Polymarket odds today. Polymarket View is independent and not affiliated with Polymarket, Kalshi or any sportsbook. Educational math, not financial or betting advice.