Rex says
The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.
Try a scenario
Click to load — tweak from there.Inputs
Result
Estimated risk of ruin
28.89%
Estimated survival probability
71.11%
Per-bet edge
1.18%
Bankroll measured in bet-sized units
50.0
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How to use this
- 1Enter win probability (%).
- 2Enter odds per bet (american).
- 3Enter bet size as % of bankroll (%).
- 4Read your estimated risk of ruin on the right — it updates as you type.
- 5Hit Share to keep the scenario or send it to someone.
About this calculator
Risk of ruin is the probability that a betting strategy eventually drains your entire bankroll to zero, given your edge, the odds you're betting at, and how large a fraction of your bankroll you stake per bet. Even a real, documented edge can carry a meaningful chance of ruin if you bet too large a fraction of your bankroll per wager — this is the entire reason Kelly-style fractional staking exists. This calculator uses the classic gambler's ruin approximation for a bettor with a positive edge, based on your win probability, the payout odds, and your bet size as a fraction of bankroll, to estimate the probability of hitting zero before the strategy meaningfully compounds your bankroll. A 55% win rate at even-money bets sized at a full 10% of bankroll per wager carries dramatically more ruin risk than the same edge sized at 2% per wager. The output is a modeled estimate, not a guarantee — real bankrolls also face bet limits, line movement, and streaks that don't perfectly follow the idealized independent-trial assumptions here.
Worked example
Using the values the calculator loads with:
Inputs
- Win probability: 53 %
- Odds per bet (American): -110
- Bet size as % of bankroll: 2 %
Results
- Estimated risk of ruin: 28.89%
- Estimated survival probability: 71.11%
- Per-bet edge: 1.18%
- Bankroll measured in bet-sized units: 50
What each field means
Inputs
- Win probability (%)
- The win probability used in the calculation, measured in %. Starts at 53 % so you have a working example on load. Accepted range: 1–99 %.
- Odds per bet (American)
- The odds per bet (american) used in the calculation. Starts at -110 so you have a working example on load.
- Bet size as % of bankroll (%)
- The bet size as % of bankroll used in the calculation, measured in %. Starts at 2 % so you have a working example on load. Accepted range: 0.1–50 %.
Results
- Estimated risk of ruin
- Returned as a percentage and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Estimated survival probability
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Per-bet edge
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Bankroll measured in bet-sized units
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
What does 'risk of ruin' actually mean in practice?
It's the modeled probability that a losing streak, even while betting a genuine edge, wipes your bankroll to zero before your edge has a chance to compound it upward. It's not about whether your strategy is profitable on average — it's about whether variance kills you before the average plays out.
Why does bet size matter so much if my edge stays the same?
Ruin risk shrinks roughly exponentially as bet size drops, because each bankroll unit takes more consecutive losses to exhaust. Cutting your bet size from 5% to 2% of bankroll per wager can turn a double-digit ruin probability into a fraction of a percent, without changing your edge at all — this is the core argument for flat, small unit sizing.
How does this relate to the Kelly criterion?
Full Kelly sizing is mathematically designed to maximize long-run bankroll growth, but it does so with real, sometimes uncomfortable ruin-adjacent volatility. Betting a fraction of Kelly (commonly half or quarter Kelly) sacrifices some growth rate in exchange for a meaningfully lower risk of ruin, which is why most practitioners size below full Kelly.
What if my edge estimate is wrong?
This is the biggest real-world risk this model doesn't capture: it assumes your win probability input is accurate. If your true edge is smaller than you believe, or negative, the actual risk of ruin is far higher than this calculator shows, because a mis-estimated positive edge that's actually near zero or negative approaches near-certain eventual ruin at any consistent bet size.
Accuracy and limitations
- Results are rounded for display; the underlying calculation keeps full precision.
- Very large or very small inputs may hit floating-point limits in the browser.
- Inputs outside the accepted range are clamped rather than rejected.
Related tools
Betting Unit Size Calculator
Turn your bankroll into a consistent flat unit size for disciplined staking.
Expected Value (EV) Bet Calculator
Find the dollar EV of a wager given your true win probability.
Break-Even Win Rate Calculator (-110 and Beyond)
The win percentage you need at any odds just to break even.
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Bankroll Risk of Ruin Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/risk-of-ruin-bankroll-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/risk-of-ruin-bankroll-calculator" target="_blank" rel="noopener">Bankroll Risk of Ruin Calculator — RevenueLab</a> (2026).</p>
Source: [Bankroll Risk of Ruin Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/risk-of-ruin-bankroll-calculator) (2026).