Turn decimal odds into true percentage chances and measure the bookmaker margin on any market.
Implied probability is what the odds say about the chance of an outcome: one divided by the decimal price. At 4.00 the market implies 25%; at 1.25 it implies 80%. If your own estimate differs from the implied number, that difference is your edge — or your mistake.
The tool also totals the implied probabilities across a market. Anything above 100% is the bookmaker margin, and it is the single most useful number for judging whether a book is worth betting into.
A two-way market with a 2% overround is competitive; 8% is expensive. Because the margin compounds across every bet you place, a book two points tighter is worth more over a season than any welcome bonus.
Prediction markets are a useful benchmark here: they price probabilities with fees rather than a spread, so a liquid market gives you a near-margin-free reference.
Add the implied probabilities of every outcome in a market. A fair market sums to 100%; a real one sums to more, and the excess is the bookmaker’s margin expressed as a percentage of a certainty.
That figure is the single most useful number for comparing books, because it is the cost you pay regardless of which side you take. A market at 102% is charging roughly a fifth of what a market at 110% charges.
No. It is the market’s price, which includes the bookmaker’s margin and any bias in how the money is distributed.
Normalise the implied probabilities so they sum to 100% — that is exactly what the no-vig calculator does.