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Ten calculators covering the math that actually decides whether a bet is worth making — converting prices, stripping out the bookmaker's margin, sizing a stake properly, and working out what you'd need to hit to break even. No signup, no account, nothing stored.
American, decimal, fractional and implied probability are four ways of writing the same price. Type any one.
Both sides of a market always add up to more than 100%. That surplus is the book's cut. Strip it out to see the true price.
How much edge the sportsbook has baked into a two-sided market. Lower is better for you.
Standard two-way markets run about 4–5%. Anything under 3% is a sharp price; over 6% and you're paying well over the odds.
The percentage of bets you need to win at a given price just to break even. Anything below it loses money long-term.
What a bet is worth on average if you could make it over and over. Positive EV means the price is in your favor.
The hard part isn't this math — it's the probability estimate. Garbage in, garbage out.
Compare your own probability against the no-vig market price to see how much of an edge you actually have.
The mathematically optimal bet size for a given edge. Most people should use a fraction of it — full Kelly swings hard.
If Kelly returns zero or negative, the bet has no edge at your stated probability and shouldn't be made at all.
What a multi-leg bet actually returns, and the true combined probability you're betting on.
You're holding a live ticket and want to lock in a result. This is how much to put on the other side.
Flat staking at a given unit size — how far a normal losing run can take you down. Variance is bigger than people expect.
A 10-bet losing run is completely normal even for a winning bettor. Size so it's survivable, not so it's profitable if you never lose.
The same math applied to real games — with the reasoning shown, on every game on the board.
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