What edge means in betting, and how to calculate it

In sports betting, edge means how much a bet is worth above or below what it costs, as a percentage of the stake. A 3% edge means that if you could place the same bet many times you would make $3 per $100 staked on average. It does not mean this bet wins: a 3% edge on an even-money game still loses almost half the time. Edge is the same number as expected value expressed per dollar, and the book has one too: on most bets the edge is the book's, and it is called the hold.

The formula

Edge = fair probability × decimal odds − 1. The decimal odds are what your book pays per dollar, stake included (+110 is 2.10, −110 is 1.909). The fair probability is the chance the bet really wins, which nobody knows exactly; the practical estimate is a sharp market's price with the margin taken out, which is what devigging does. The same formula can be written as fair probability ÷ your price's implied probability − 1, which gives an identical answer.

The book's edge: why −110 is −4.5%

Run the formula on an ordinary bet. A game priced −110 on both sides has a fair probability of 50% each way, and −110 pays 1.909 per dollar, so the edge is 0.50 × 1.909 − 1 = −4.5%. That −4.5% is the book's hold seen from your side of the counter, and it is why betting at random loses about that much per dollar over time. The hold and vig guide works it for three-way markets. A positive edge means finding a price that more than pays back that margin, usually because one book has not moved when the sharper market has.

Edge in dollars, and how it sizes a bet

Expected profit in dollars is stake × edge: $250 at a 4.8% edge is $12.00 on average. Edge also drives stake size. The Kelly criterion stakes edge ÷ (decimal odds − 1) of your bankroll, so the 4.8% edge at +130 is 0.048 ÷ 1.30 ≈ 3.7% of bankroll at full Kelly. Because every edge is an estimate, most bettors who last stake a quarter of that or less — about 0.9% here.

How to calculate your own edge as a bettor

There are two ways, and only one of them is quick. The first is your results: profit divided by total staked over every bet. It is the number that pays, but it is noisy, and at a 3% edge it takes thousands of bets before it separates from luck (the variance guide has the table). The second is closing line value: run the same formula with the market's devigged closing probability in place of your estimate. If you took +130 and the market closed with that side at a fair 46.5%, your edge against the close was 0.465 × 2.30 − 1 ≈ +7.0%. Averaged over 50–100 bets, that tells you whether your prices are beating the market long before results can. The CLV guide explains why the close is the benchmark.

Edge, arbitrage and promos

Edge describes a single bet against its fair price. An arbitrage is different: two or more bets covering every outcome, priced so the combined return is the same whichever wins, so it does not depend on a fair-price estimate at all. Promotions change the formula's inputs rather than the idea — a profit boost raises the decimal odds, a bonus bet removes the stake from the payout — and the same fair-probability arithmetic values them.

Where TrueEdge shows it

The Positive EV board runs this calculation across every sportsbook and exchange price it reads: each market is devigged against the sharper books, and prices that beat the fair number by enough to clear its floor are listed with their edge and a fractional-Kelly stake. The edge it shows is an estimate built from the fair price, not a promise, and the Hold Calculator runs the devig step on any market you paste in, free.