Betting Calculators
Free tools for smarter betting. Convert odds, calculate arbitrage profit, and size your bets with the Kelly Criterion.
Odds Converter
Enter odds in any format and instantly see the equivalents in all formats plus 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.
Kelly Criterion Calculator
Calculate the optimal bet size based on your estimated probability and the odds offered. Maximize long-term growth while minimizing risk of ruin.
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.