Free tools for smarter betting. Convert odds, calculate arbitrage profit, find bookmaker margins, 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:
Payout Calculator
Quickly calculate your potential profit, total payout, and return on investment (ROI) for any bet. Enter decimal odds and your stake.
2-Way Arbitrage Calculator
Enter the best odds for each of two outcomes (e.g. tennis, basketball) to calculate your guaranteed profit. The calculator divides your total stake proportionally.
3-Way Arbitrage Calculator (Soccer / Football)
For events with three outcomes — Home Win, Draw, Away Win — like soccer matches. Enter the best odds from different bookmakers for each outcome to find guaranteed profit.
Overround & Margin Calculator
Calculate the bookmaker's margin (overround/vig) for any market. Enter the odds for all outcomes to see implied probabilities, the bookmaker's edge, and fair odds with vig removed.
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.
Payout Calculation
Profit: stake × (decimal − 1)
Total Payout: stake × decimal
ROI: (decimal − 1) × 100%
Arbitrage Profit
Combined implied probability (2-way): (1 ÷ odds₁) + (1 ÷ odds₂) — must be below 1.0 (100%)
Combined implied probability (3-way): (1 ÷ odds₁) + (1 ÷ odds₂) + (1 ÷ odds₃) — must be below 1.0 (100%)
Profit %: (1 ÷ combined_implied − 1) × 100%
Stake per outcome: (total_stake × (1 ÷ odds_n)) ÷ combined_implied
Overround & Vig
Overround: total implied probability − 100% — the bookmaker's built-in edge
Vig (Juice): (overround ÷ (1 + overround)) × 100% — the bookmaker's commission on each bet
Fair odds: actual odds × total implied probability — removes the vig to show true probability odds
A market with 0% overround is "fair" — negative overround indicates a potential arbitrage opportunity
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.