Free Betting Tools
Free calculators for odds, implied probability and bookmaker margins. No signup required.
Odds Converter
Convert between decimal, fractional, American odds and implied probability instantly.
Use tool →Arbitrage Calculator
Check whether the best prices across bookmakers imply a total probability under 100%, and see the stake split.
Use tool →Margin Calculator
Calculate bookmaker margin, overround and fair odds for any betting market.
Use tool →Kelly Criterion Calculator
Apply the Kelly Criterion formula to a price and a probability estimate. Includes fractional Kelly options.
Use tool →What these calculators do
These four tools cover the everyday maths of odds. The odds converter translates between decimal, fractional and American formats and shows the implied probability behind any price. The margin calculator reveals how much overround a bookmaker has built into a market, so you can see what fair odds would look like.
The other two work across prices. The arbitrage calculator checks whether the best odds for every outcome, taken from different bookmakers, imply a total probability under 100%, and shows how a stake would split across them. The Kelly criterion calculator applies the Kelly formula to a price and a probability estimate, with fractional Kelly options that scale the result down.
They are useful for analysts comparing prices, researchers modelling markets, and developers sanity-checking their own calculations. If you want to automate any of this, the same numbers are available programmatically: our API covers odds from 450+ bookmakers across 34 sports.
See how we compare to other odds APIs: vs The Odds API · vs BetsAPI · vs OpticOdds