BetCalc
Parlay payouts, implied probability, Kelly criterion, arbitrage detection, and hold percentage. The math behind the bet.
Parlay Calculator
Calculate parlay payouts for 2-15 legs. American, decimal, or fractional odds.
Implied Probability Calculator
Convert betting odds to implied probability. American, decimal, and fractional formats.
Kelly Criterion Calculator
Calculate optimal bet size using the Kelly criterion for bankroll management.
Arbitrage Calculator
Detect arbitrage opportunities and calculate stake distribution for guaranteed profit.
Hold Percentage Calculator
Calculate a bookmaker's hold (vig/juice) from the odds on all outcomes.
About BetCalc
BetCalc provides free sports betting math tools. Calculate parlay payouts, convert between odds formats, find implied probabilities, optimize bet sizing with Kelly criterion, and detect arbitrage opportunities.
All tools run in your browser — no data is sent anywhere, no account required. These calculators are for educational and analytical purposes.
Odds formats: American odds (+/−), decimal odds, and fractional odds all express the same probability differently. American odds +150 means a $100 bet profits $150 (return $250 total); −150 means bet $150 to profit $100. Decimal odds = (American positive odds / 100) + 1 for positive odds; for negative odds, decimal = (100 / |American|) + 1. Fractional odds = decimal − 1, expressed as a ratio (e.g., 3/2 = 1.5 decimal = +150 American).
Expected value (EV) is the theoretical return per dollar wagered over the long run: EV = (probability of winning × payout) − (probability of losing × stake). A positive EV bet has a mathematical edge over the sportsbook. Finding positive EV requires estimating true probabilities more accurately than the market price reflects — which is difficult and not guaranteed to produce short-term profits even with a real edge.
Kelly Criterion for bet sizing: f = (bp − q) / b, where b = net decimal odds (decimal odds minus 1), p = your estimated win probability, q = 1−p. The output f is the fraction of your bankroll to bet. Most professionals use 1/4 to 1/2 Kelly to reduce variance from estimation errors — full Kelly is theoretically optimal only with perfect probability estimates.
Responsible gambling: all sports betting calculators on this site are educational tools. The house maintains a mathematical edge through the vig (overround) built into the odds. Consistently beating closing line value across hundreds of bets is the only reliable indicator of a long-term edge. Set time and money limits before betting, and never chase losses. If gambling causes financial or personal harm, contact the NCPG Helpline: 1-800-522-4700.