Bettor Ed Kelly Bet Sizer

• What is a Kelly Bet Sizer?

  • The Kelly Bet Sizer is a free sports betting calculator that uses the Kelly Criterion to determine your optimal bet size based on your edge, odds, and bankroll. The Kelly Criterion is a proven mathematical betting strategy used by professional bettors and investors to maximize long-term bankroll growth while controlling risk.
    Simply enter your odds, win probability, and bankroll to see the percentage or dollar amount you should wager for maximum expected growth — whether you’re betting on FanDuel, DraftKings, BetMGM, or other sportsbooks.

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• What do the Input Fields mean?

  • Each input field in the Kelly Bet Sizer helps you customize how your bets are modeled:

  • Event Type – Choose whether bets are independent (different games) or mutually exclusive (only one can win, like a horse race).

  • # of Events / Outcomes – Enter the number of bets or outcomes you want to include (up to 10).

  • Consecutive Series – The number of times you plan to repeat your betting sequence (for example, 18 NFL weeks).

  • Kelly Multiplier – Adjusts your risk level:

  • 1 = Full Kelly (maximum growth rate)

  • 0.5 = Half Kelly (moderate risk)

  • 0 = No risk

  • 2+ = More aggressive than Kelly

  • Starting Bankroll – Your bankroll before the first bet. Use “1” to express bet sizes as percentages.

  • Odds (Event X) – Enter the sportsbook odds for each event in American (-110) or Decimal (1.91) format.

  • Win % (Event X) – Your estimated probability of winning, in percentage form (e.g., 55 for 55%).

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• How do you calculate the Kelly bet size?

  • The Kelly Criterion formula calculates your optimal bet size as a percentage of your bankroll using this process:

  • Step 1: Convert odds to decimal format (if needed)

    • For positive American odds: Decimal Odds = (Odds + 100) / 100

    • For negative American odds: Decimal Odds = (Absolute Odds + 100) / Absolute Odds

  • Step 2: Calculate your Edge (Expected Value)
    Edge = (Probability × Decimal Odds) − 1

  • Step 3: Determine your Kelly percentage
    Kelly % = Edge / (Decimal Odds − 1)

  • Step 4: Apply your bankroll and multiplier
    Bet Size = Edge × Bankroll × Kelly Multiplier

    • For example, if you estimate a 55% win probability at -110 odds, your full Kelly bet would be around 5% of your bankroll. Using Half Kelly (0.5 multiplier) would risk about 2.5%.

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• How does this calculator help me?

  • The Kelly Criterion Calculator helps you bet smarter, not bigger. It identifies your mathematically optimal stake size — maximizing your expected bankroll growth while minimizing risk.
    By adjusting your Kelly Multiplier, you can choose a risk level that fits your comfort zone. Most sharp bettors use a fractional Kelly (0.25–0.5) to smooth out short-term variance and avoid large drawdowns.
    This tool is perfect for bettors who track performance, use models, or compare odds across U.S. sportsbooks like FanDuel, DraftKings, or offshores like BetOnline.

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