How the Kelly Criterion Calculator Works
The Betstamp Kelly Criterion Calculator returns the optimal stake size for any bet based on your edge and bankroll. Enter your Kelly multiplier (for fractional Kelly sizing), the sportsbook's odds, your estimated win probability, the true odds, and your bankroll — the calculator outputs the recommended stake in both dollars and as a percentage of bankroll.
How to Use the Kelly Calculator
- Enter your Kelly Multiplier (1.0 for full Kelly, 0.5 for half Kelly, 0.25 for quarter Kelly — recommended starting point)
- Enter the sportsbook's Odds (e.g., +110)
- Enter your Win Probability (e.g., 55%)
- Enter the True Odds from your devigged reference market
- Enter your Bankroll (e.g., $10,000)
- The calculator returns:
- Kelly Stake: the recommended bet size in dollars
- Kelly Percentage: the stake as a percentage of your bankroll
If your inputs show no edge or a negative edge, the calculator will return a $0 stake. Kelly never recommends betting without an edge.
What the Kelly Multiplier Does
This is one of the most important features of the Betstamp Kelly Calculator. The Kelly Multiplier lets you scale the output to match your risk preference:
- Multiplier = 1.0 (Full Kelly): maximum growth, maximum variance — assumes your probability estimates are exactly right
- Multiplier = 0.5 (Half Kelly): ~75% of full Kelly's long-term growth with half the variance
- Multiplier = 0.25 (Quarter Kelly): ~55% of full Kelly's growth with a quarter of the variance — the most commonly used setting for serious bettors
- Multiplier = 0.1–0.2: very conservative; recommended when your probability estimates are unproven
Full Kelly is mathematically optimal if your win probability estimates are perfect. In practice, nobody's estimates are perfect — and full Kelly produces brutal drawdowns. Fractional Kelly is how professionals actually bet.
The Kelly Criterion Formula
The math behind the calculator:
Kelly % = [(Decimal Odds × True Probability) – 1] ÷ (Decimal Odds – 1)
The calculator then multiplies the output by your Kelly Multiplier and your bankroll to get the final stake.
Example: Bankroll $10,000, odds +110 (decimal 2.10), estimated true probability 55%, Kelly Multiplier 0.25.
- Full Kelly %: [(2.10 × 0.55) – 1] ÷ 1.10 = 14.1%
- After 0.25 multiplier: 3.5%
- Kelly Stake: $350
When Kelly Tells You NOT to Bet
If the formula returns zero or negative, the calculator outputs a $0 stake. This happens when:
- The sportsbook's odds are worse than your estimated true odds
- Your win probability estimate is lower than the implied probability of the odds offered
- There is no edge — the bet is -EV or neutral
In those cases, Kelly's answer is simple: don't bet.
Origin of the Kelly Criterion
The Kelly Criterion was introduced in 1956 by John L. Kelly Jr., a researcher at Bell Labs. Originally developed to solve a communication problem (maximizing information transmission rates over noisy channels), it was quickly adopted by gamblers and investors who realized its mathematical power for managing risk.
Ed Thorp (blackjack card-counting pioneer and hedge fund manager) popularized Kelly in financial markets. Warren Buffett's position sizing at Berkshire Hathaway has been described as roughly Kelly-based.
How to Use Kelly With Other Betstamp Tools
The standard sharp bettor workflow:
- Betstamp PRO identifies a +EV bet by comparing a soft book's price to a devigged sharp-book line
- Verify the edge in the Expected Value Calculator — confirms the bet is profitable
- Kelly Calculator tells you exactly how much to stake (most pros use 0.25 or 0.5 multiplier)
- Track the bet in Betstamp to measure long-term ROI and CLV
With Betstamp PRO—the most advanced top-down betting odds screen in the market. Bettors will find hundreds of daily betting edges with ease, allowing you to scale your profits long-term. Click the banner to book a free demo.
