Bankroll management for sports betting: the unit system, explained

Most people who lose money on sports don't lose it on bad picks. They lose it on bad sizing. A good read with the wrong stake can still wreck you, and a mediocre read with a disciplined stake usually just costs a little. Bankroll management is the unglamorous part of this, and it is the part that decides whether you are still around in March.

Start with the bankroll itself. It is a set amount of money you have decided, in advance, you can lose without it touching rent, bills, savings or anyone who depends on you. Not what's in your checking account. Not what you'll have after payday. A separate, fixed number. If losing all of it would change your month, it's too big.

Next, the unit. A unit is a fixed slice of that bankroll, and every position you take is sized in units — not in dollars, and not in feelings. The common convention is 1% to 5% per unit, with most disciplined bettors sitting around 1% to 2%. On a $500 bankroll, a 2% unit is $10. A standard play is one unit. A play you're genuinely more confident in might be two. Nothing is ten.

Why so small? Because even a very good bettor loses a lot. We ran the numbers. Take someone who wins 55% of their plays at -110 — which would put them among the sharpest people in the market — and have them place 500 flat one-unit plays. Across 20,000 simulated runs, about 65% of those bettors hit a losing streak of seven or more in a row at some point. About 31% were still down after their first 100 plays. The median worst drawdown, peak to valley, was around 16 units, and one in ten saw 27 units or more. That is a winning bettor. Their expected profit over those 500 plays is about 25 units, and they still spent long stretches underwater.

Now change only the stake size for that same 55% bettor. Staking 2% of the current bankroll per play, virtually none of our simulated runs (about 1 in 10,000) ever fell below a quarter of the starting bankroll. At 5% per play, about 7% of runs did. At 10%, nearly half did — 47% — and the typical ending bankroll was worse than at 5%. At 25% per play, 98% of runs fell below a quarter of the bankroll, and the typical ending bankroll was effectively zero. Same picks. Same edge. The only thing that changed was how much rode on each one.

There's real math behind this. In 1956, John Kelly at Bell Labs published a formula for the stake size that grows a bankroll fastest over time when you know your edge. For our 55% bettor at -110, it works out to about 5.5% per play. Bet more than that and long-run growth goes down, not up. Bet double it and you can grind a real edge down to nothing. The catch is the phrase "when you know your edge." Nobody knows their true win rate going into a season, and overestimating it is the most common mistake in the game. That's why experienced bettors use a fraction of Kelly — a quarter or a half — or simply a flat 1% to 2% unit. You give up a little upside so that a bad month can't end you.

A few rules that make the system work.

Decide the unit before the slate, not during it. Write it down. Reset it on a schedule — once a month is fine — not after every win or loss.

Size by conviction, inside a tight band. One unit standard, two for your strongest spots. If a play feels like five units, that's a feeling, not an edge.

Keep a record. Every play, the price you got, the stake, the result. Your memory will keep the wins and lose the losses. A spreadsheet won't.

Don't top up in a downswing. If the bankroll is down, the unit shrinks with it. Adding fresh money to "get back" is the start of chasing, which has its own read here.

Treat withdrawals as part of the plan. If the bankroll grows well past where it started, taking some off the table isn't weakness. It's the point.

None of this makes any single play more likely to win. What it does is keep you alive long enough for an edge — if you have one — to show up in the numbers. Everything on the board here is research and opinion, not a guarantee. Size it like it could lose, because some of it will.

If betting has stopped being fun, or you're spending more than you planned, the National Problem Gambling Helpline is free, confidential and open 24/7: call or text 1-800-MY-RESET (1-800-697-3738). 21+ only.