01How to use these tools
Start with the odds converter if the prices you see aren't in decimal. Then use the fair odds calculator on a full market from one bookmaker: the result is the market's own view of the true chances, with the margin taken out. Finally, put that fair price (or your own estimate) into the EV calculator next to the best odds you can find. If EV comes out positive, the price is bigger than the probability deserves.
Every calculator updates as you type and keeps your numbers in the page address, so you can bookmark a calculation or send it to someone.
02The formulas in one place
Implied probability = 1 / decimal odds
Margin % = (sum of implied probabilities - 1) x 100
Fair probability = implied probability / sum of implied probabilities (multiplicative method)
EV = (your probability x decimal odds) - 1Each calculator page explains its formula in full, with worked examples.
03Frequently asked questions
Are these calculators free?
Yes. There's no sign-up and no limit. They run in your browser, so they're instant and keep working on a slow connection once the page has loaded.
Do you store the numbers I type?
No. Nothing is sent to a server. Your inputs only live in the page address, which is what makes a calculation shareable. If you don't share the link, nobody sees it.
Which calculator should I start with?
If you already have your own probability for a bet, go straight to the EV calculator. If you don't, use the fair odds calculator on a full market first. Its fair odds are a reasonable starting estimate, and you can then compare them with other bookmakers' prices.
How does this relate to JOPP?
JOPP runs the same maths on every player market in every match, with its own model for the fair odds, and compares them with Kambi and Bet365 every 15 minutes. These tools let you do it by hand for one bet at a time.