Odds and Betting calculator
A free suite of sports betting calculators designed for value bettors and exchange traders. Convert decimal odds to implied probability, find the equivalent lay stake for any back bet on Betfair or Smarkets, calculate your true odds after exchange commission, and size your bets optimally with the Kelly Criterion staking formula. All tools update in real time — no sign-up required.
Odds Probability Converter
Use our free odds-to-probability converter to instantly calculate the implied probability behind any decimal odds. Knowing the implied probability is the foundation of value betting: the higher the probability of an event, the lower the odds offered by the bookmaker. Enter either value and the other updates automatically.
Back Lay Converter
Convert any back bet to its equivalent lay on betting exchanges like Betfair or Smarkets with our free calculator.
- Back: The standard sports bet — you stake in favour of an event occurring.
- Lay: You take the bookmaker’s side, betting against the event. Every back bet has a direct lay equivalent at the same implied probability.
Commission Calculator
Calculate your true odds after betting exchange commission with our free tool. Platforms like Betfair and Smarkets charge 3–6% commission on winning bets, which directly reduces your effective odds. Enter the market odds and your commission rate to find the real value of your bet before placing it.
Stake Calculator
The Kelly Criterion calculator finds the mathematically optimal stake to maximise long-term bankroll growth. Widely used in professional sports betting, this staking formula weighs potential profit against risk of ruin using your assessed probability, the available odds, and your current bankroll. Overbetting and underbetting both reduce expected growth — Kelly finds the exact sweet spot.
