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Kelly Criterion Calculator

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Determine the mathematically optimal stake size to maximize long-term bankroll growth while managing risk.

How to use this tool

The Kelly Criterion balances Risk (Loss probability) vs Reward (The odds).

1. Enter your total Current Bankroll.

2. Enter the Decimal Odds available (e.g., 3.0 for 2/1).

3. Enter your Estimated Win % (This is your "Edge". Be honest!).

4. Select a Kelly Mode (Half Kelly is recommended for safety).

Why Smart Bettors Use the Kelly Criterion

The biggest mistake most punters make isn't picking the wrong horse—it's betting the wrong amount. You could pick winners all day, but if you bet too little, your bankroll won't grow. If you bet too much, a short losing streak will wipe you out.

The Kelly Criterion solves this mathematically. It calculates the exact percentage of your bankroll you should risk based on the Edge you have over the bookmaker.

Full Kelly vs. Half Kelly: Honest John's Advice

You will notice a dropdown in the calculator for "Kelly Mode." Here is the difference:

  • • Full Kelly: The mathematically fastest way to grow wealth, but it is a wild ride. It can suggest huge stakes (e.g., 20% of your bank) on a single horse. If you hit a losing streak, your bankroll crashes hard.
  • • Half Kelly (Recommended): This simply halves the recommended stake. It gives you about 75% of the maximum growth potential but with 50% less volatility. For most serious bettors, this is the "Sweet Spot."

How to estimate your "Win Chance"

The calculator is only as good as the data you put in. You need to estimate the true probability of the horse winning.

Example: If a horse is priced at 2/1 (3.0), the bookie is implying it has a 33% chance of winning. If your analysis (using Patternform or speed ratings) suggests the horse actually has a 50% chance, you have an "Edge." Enter 50% into the calculator, and it will tell you how much to bet to exploit that gap.

Where to go next?

Now you know your stake size, use our other tools to place the perfect bet.

Split Stake (Dutching) → Trade Out Calculator → Each Way Saver →

Disclaimer: This calculator is provided for educational purposes only. The Kelly Criterion is a mathematical formula for optimal growth, but it relies entirely on the accuracy of your estimated "Win Chance." If you overestimate your edge, the formula can suggest dangerous stakes. Honest John Tipster accepts no liability for losses. Always gamble responsibly.