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How to Use the Kelly Criterion to Size Your Horse Racing Bets

Learn how the Kelly Criterion helps you bet smarter by balancing risk and reward — perfect for value-focused betting at MyWinners.

Written by Rob Lawson

You’ve found a great bet. Now what? How much should you stake? Bet too much and a loss hurts. Bet too little and you waste a rare opportunity. The Kelly Criterion gives horse racing bettors a formula to size bets based on value — so you win more when you’re right and survive the times you’re wrong. It’s risk management, but with teeth.

What is the Kelly Criterion?

The Kelly Criterion is a mathematical formula that helps you decide how much to wager on a bet based on two things:

  • Your edge (how much value the bet has)

  • The odds (your return if it wins)

The basic idea:
The bigger your edge, the bigger your bet — but always proportionally to your bankroll.

How it works (simple version)

Let’s say you think a horse has a 40% chance to win, and it’s going off at 3-to-1 (25%) odds. You have an edge.

Kelly’s formula says bet:

(Edge × Odds) / (1 + Odds)
So: (0.40 - 0.25) × (3) Ă· (1 + 3) = 0.1125 → 11.25% of your bankroll

If your bankroll is $200, bet $22.50.
No guessing. Just math.

Why it’s useful for bettors

  • Maximises long-term growth – Kelly ensures you compound winnings rather than blow up your bankroll.

  • Removes emotion – It’s a math-based staking plan, not guesswork or gut feel.

  • Focuses on value – Encourages betting only when the odds are in your favour.

When to be cautious

  • Only use Kelly when you’re confident in your estimated win percentage

  • Overestimating your edge leads to overbetting and fast losses

  • Many bettors use “half Kelly” to stay conservative

💡 Did You Know? Bill Benter used a version of the Kelly Criterion to build a horse racing model that made over $1 billion in Hong Kong. He reportedly once skipped a race because the edge wasn’t strong enough — even though he stood to win millions. Discipline over drama.

Frequently Asked Questions

Is the Kelly Criterion beginner-friendly?

It can be. Start with small bets and learn how to estimate your edge before using the full formula.

Can I use Kelly for exotic bets?

Yes — but be cautious. It’s harder to calculate your true edge on exactas or trifectas. Start with win/place/show bets.

Do I need a calculator for the Kelly Criterion?

It helps — but you can also use a Kelly calculator online or plug your values into a simple spreadsheet.

What’s the main risk of using the Kelly Criterion?

Overconfidence. If you misjudge a horse’s chances, the formula may suggest betting too much. That’s why many pros use half stakes.

Is the Kelly Criterion better than flat betting?

It can be, especially if you’re betting with a proven edge. Flat betting is simpler but doesn’t maximise growth the way Kelly does.

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