Risk of Ruin Calculator 2026

Five models, one calculator

Risk of ruin, explained

Risk of ruin is the probability that your bankroll drops to zero, or to a level you cannot recover from, before you reach your goal. Every gambler and bettor faces it, and it is the single most important number in bankroll management, because even a winning strategy busts if the bets are too big for the roll. This risk of ruin calculator on ToolsGambling is the most complete on the web: five separate models plus a Monte Carlo simulator, so whether you bet sports with a fixed edge, play poker with a win rate and variance, or size stakes by Kelly, you get the honest number. Everything here is free, with no account and no paywall on the math.

What is risk of ruin?

Risk of ruin is the chance that a run of bad variance wipes out your bankroll before your edge has time to play out. It depends on three things: how big your edge is, how large your bets are relative to your bankroll, and how much variance the game carries. A tiny edge with big bets can still ruin you; a solid edge with small bets almost never does. The counterintuitive truth is that with no edge and enough bets, ruin is certain no matter how big the bankroll, because a symmetric random walk always eventually hits zero. Only a genuine edge, staked small enough, keeps ruin below a level you can live with.

The number that changed how I bet was not my edge, it was my bet size. I once ran a 3% edge into the ground because I was staking 8% of my roll a bet, and a normal cold streak took me to zero before the edge showed up. Now I size everything so my risk of ruin sits under 5%, usually with a quarter or half Kelly, and I would rather grow slowly than get wiped out fast. This calculator exists because I wish I had run those numbers before, not after.

Why this risk of ruin calculator is different

Almost every risk-of-ruin page online runs one formula and stops. This one runs five, plus a simulator, so it fits sports betting, poker, blackjack and pure gambler's-ruin questions in a single place. Here is what ToolsGambling adds that no competitor matches.

How to use the risk of ruin calculator on ToolsGambling

Pick the model that matches your situation. For flat-staked sports betting, use advantage betting: enter your edge and your bankroll in units. For poker, use win rate and variance with your bb/100 and std/100. For Kelly staking, use the Kelly drawdown model. To see the full picture, run the Monte Carlo simulator: set your win probability, odds, stake and number of bets, and read the ruin rate, equity bands and drawdown spread. It is all free on ToolsGambling.com, with no signup.

What is a safe risk of ruin?

There is no zero, but most serious bettors and players aim to keep long-run risk of ruin at or below 1 to 5 percent. Below 1 percent is conservative and slow-growing; 5 percent is a common working ceiling; anything above 10 to 20 percent means your bets are too large for your edge and bankroll, and a normal downswing is likely to bust you. The right number is personal: it depends on how replaceable your bankroll is and how much drawdown you can tolerate without tilting. Use the inverse solve to find the bankroll or Kelly fraction that puts you where you want to be.

Risk of ruin vs risk of drawdown

Full ruin, losing everything, is actually uncommon for a disciplined bettor. The risk that bites is drawdown: a long stretch where the bankroll falls 30, 50 or 70 percent before recovering. Under full Kelly the chance of ever halving your bankroll is about 50 percent, which surprises people, while half Kelly cuts that to around 12 percent. The Kelly drawdown model and the simulator both report these numbers, because managing the drawdown you will actually experience matters more than a ruin figure you may never reach.

Risk of ruin in poker and blackjack

In poker, risk of ruin uses your win rate and standard deviation over the same sample, usually per 100 hands in big blinds, with the formula RoR equals e to the power of minus two times win rate times bankroll divided by standard deviation squared. A 5 bb/100 winner with a 100 bb/100 standard deviation and a 1000 bb roll has about a 37 percent risk of ruin, which is why poker bankrolls are measured in dozens of buy-ins. Blackjack card counters use the same diffusion idea with N0, the number of hands to overcome variance, and trip ruin for a single session. All of it comes down to the same trade: edge, bankroll and variance.

How to reduce your risk of ruin

There are only three levers. Bet smaller relative to your bankroll, which is the fastest and most reliable fix. Grow your bankroll in units, since risk of ruin falls exponentially as units rise. Or increase your edge, which is the hardest to do and the easiest to fool yourself about. Fractional Kelly does the first automatically: betting a quarter or half of full Kelly slashes drawdown risk while keeping most of the growth. Chasing losses does the opposite, raising effective stake exactly when your bankroll can least afford it.

The honest limits of any risk of ruin number

A risk of ruin figure is only as good as its inputs, and the biggest input is your edge, which most bettors overestimate. If your true edge is smaller than you think, or your win rate estimate comes from too small a sample, the real risk is higher than any calculator shows. The formulas also assume independent, identically sized bets and a stable edge, which real betting rarely delivers. Treat the output as a guide to relative risk between choices, not a promise. When in doubt, bet smaller than the math says, because the cost of being too cautious is slow growth, while the cost of being too aggressive is zero.

Common risk of ruin mistakes

The first is overestimating your edge, which makes every risk number too rosy. The second is measuring bankroll in currency instead of units, since risk of ruin depends on units, not dollars. The third is ignoring drawdown and only looking at full ruin, then quitting at a 60 percent downswing you never planned for. The fourth is full Kelly, which maximises growth but carries brutal drawdowns most people cannot sit through. The fifth is raising stakes after losses to get back to even, which is the single fastest route to ruin.

Risk of ruin terms

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On ToolsGambling.com the risk of ruin calculator is free, like every tool here. Pair it with these to size stakes, plan a bankroll and check your edge.

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