FIGHT//AI · Fights · Events · AI Picks · Fighters · Learn · About

The Kelly criterion for MMA betting

Updated 2026-10-01

Finding value is half the job. The other half is how much to put on each bet. Stake too little and a real edge earns almost nothing; stake too much and a normal losing run wipes out the bankroll. The Kelly criterion answers the question mathematically.

The formula

Kelly stake (as a share of your bankroll) = (p × d − 1) / (d − 1), where p is the win probability and d the decimal odds. The top of the fraction is the expected value; the bottom is the net odds.

Example: 45% at 2.50. Kelly = (0.45 × 2.50 − 1) / 1.50 = 0.125 / 1.50 = 8.3% of the bankroll.

When the EV is zero or negative, Kelly says stake nothing – the formula itself filters out bad bets.

Why nobody bets full Kelly

Full Kelly maximises long-run growth only if your probabilities are exactly right. They never are. If you overrate your edge, full Kelly overbets, and the swings are brutal: halving the bankroll along the way is normal.

That is why most professionals use a fraction – half or a quarter Kelly. A quarter Kelly keeps most of the growth while cutting the swings dramatically. FIGHT//AI's AI picks use quarter Kelly on a 100-unit bankroll, with a cap on any single bet.

Caps and long shots

Two extra rules make Kelly safer in MMA. First, cap the stake on any single fight, so one bad read cannot do serious damage. Second, cut the stake on long odds: an underdog at 4.00 or more can have a real edge and still lose many times in a row.

  • Use a fraction of Kelly (¼ to ½).
  • Cap any single bet (for example 10% of the bankroll).
  • Reduce stakes on long shots.
  • Recalculate stakes from the current bankroll, not the starting one.

Units and bankroll

Bettors talk in units so results compare across bankrolls. If your bankroll is 1,000 and you set 1 unit = 10, a 2.5-unit bet is 25. FIGHT//AI's track record is in units on a 100-unit bankroll, and the AI picks page lets you switch to your own bankroll and staking method.

Only bet money you can afford to lose. Betting is for adults (18+); if it stops being fun, stop.

Keep reading