Expected Value (+EV) Betting: How to Calculate Your Edge

Expected value (EV) is the average result of a bet if you could place it over and over. A positive-EV, or +EV, bet is one where the price you're offered is better than the fair probability of the outcome. Finding +EV is the whole game, and it starts with a trustworthy estimate of fair probability.

The expected value formula

For a bet at decimal payout b (your profit per $1 staked) with true win probability p, expected value per dollar is EV = p · b − (1 − p). If that number is positive, the price is in your favor; if negative, the book has the edge. The entire difficulty is estimating p honestly.

Where fair probability comes from

You can't use the same book's price as your probability estimate. It already contains the vig, and it's the thing you're trying to beat. The standard approach is to de-vig a sharp book's line (the sharpest public estimate) and treat that fair probability as the benchmark. When a softer book's price implies a probability meaningfully below that benchmark, the difference is your edge.

This is why +EV and de-vigging are two halves of one method: de-vig the sharp line to get p, then test a soft price against it.

How big is a real edge?

Genuine +EV edges are usually small, on the order of 1% to 4% per dollar. That matters for two reasons. First, small edges need large samples before they show up in your win rate, so short-term results tell you almost nothing. Second, an edge that size is the same magnitude as ordinary line movement, so a +EV price goes stale within minutes. Speed and an accurate benchmark are everything.