Betting Calculators

Free tools for smarter betting. Convert odds, calculate arbitrage profit, and size your bets with the Kelly Criterion.

Odds Converter

Enter any odds format and instantly see the equivalent in all other formats, plus the implied probability.

American: —Fractional: —Implied Probability: —

Arbitrage Profit Calculator

Enter the best odds for each outcome to calculate your guaranteed profit. The calculator divides your total stake proportionally across all outcomes.

Enter odds and stake, then click Calculate.

Kelly Criterion Calculator

Calculate the optimal bet size based on your estimated probability and the odds offered. The Kelly Criterion maximizes long-term bankroll growth while minimizing risk of ruin.

Enter odds, probability, and bankroll, then click Calculate.

Formulae Explained

Odds Conversion

  • Decimal to American: If decimal >= 2.00 → +((decimal - 1) * 100). If decimal < 2.00 → -(100 / (decimal - 1)).
  • Decimal to Implied Probability: (1 / decimal) * 100%
  • American to Decimal: If positive → (American / 100) + 1. If negative → (100 / |American|) + 1.

Arbitrage Profit

  • Combined implied probability: (1 / odds₁) + (1 / odds₂) — must be below 1.0 (100%)
  • Profit %: (1 / combined_implied - 1) * 100%
  • Stake per outcome: (total_stake * (1 / odds_n)) / combined_implied

Kelly Criterion

  • Fraction: f* = (b * p - q) / b, where b = net odds (decimal - 1), p = win probability, q = 1 - p
  • Optimal stake: bankroll * f*
  • Half Kelly: Often recommended to reduce variance — stake half the Kelly fraction.

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