Betting Edge Calculator

Edge is the difference between what you think will happen and what the price says will happen. Enter both and this shows the gap three ways, because “edge” means three different things in practice and people routinely confuse them.

Probability edge is the raw difference in percentage points. You say 55%, the price says 50%, the edge is five points. It is the most intuitive figure and the least useful for comparing bets, because five points means something completely different on a favourite than on a longshot.

Expected ROI is what those points are worth per dollar staked. This is the number that compares. Five points of edge at even money is +10% ROI; five points on a 10% shot is +50% ROI, because you are collecting a much longer price on the occasions you are right. Same edge, five times the return.

Relative edge sits between them — your probability as a proportion of the implied one. It is the honest way to describe confidence on longshots, where a one-point edge can be a 20% improvement on the price.

All three depend entirely on the probability being yours and being better than the market’s. That is the hard part, and no calculator does it for you. If your estimate is anchored to the price you are testing it against, the edge is an artefact of the anchoring rather than a finding. The most reliable check is whether your number came from a process you had before you saw the line.

A coin-flip market at +100 where you make the side 55%. The price implies 50%, so the point edge is +5.00 pointsand the expected ROI is 0.55 × 2.00 − 1 = +10%.

Now a longshot at +900 where you make it 15% against an implied 10%. The point edge is identical — five points — but the ROI is +50%, five times larger. Every dollar staked is worth five times as much.

That gap is why point edge is a poor way to rank bets. It is also why longshot edges deserve more scepticism: getting a 10% market to 15% requires knowing something quite specific, and small errors in small probabilities are proportionally enormous.

What is a realistic edge?

For a serious bettor beating closing lines, one to three percentage points against a sharp market is a genuine, sustainable edge. Anything above about five points on a liquid market usually means the model is wrong, not that the market is.

Why does the same edge produce different ROI?

Because ROI depends on the price you collect when you are right. Five points of edge at even money returns 10%; the same five points on a 10% shot returns 50%, since the winning payout is nine times larger.

Should I rank bets by edge or by ROI?

By ROI when you are comparing which bet is worth more per dollar. By Kelly fraction when you are deciding how much to stake, since that also accounts for the risk of the price. Point edge is the least useful of the three for either decision.

The implied probability includes the vig — is my edge overstated or understated?

Understated, if you are comparing against a single price. The book’s implied probability is inflated by its margin, so a bet showing zero edge against the raw price actually has a small edge against the fair price. The no-vig calculator gives you that fair number.

Where should my probability come from?

Anywhere except the price you are testing. A model, a power rating, a sharp book’s no-vig line, or a documented process — but not a number you formed after looking at the line, which produces edges that exist only in the anchoring.

• Expected Value in Sports BettingThe one number that decides whether a bet is worth making — and why it says nothing at all about whether this particular bet wins.11 min read

• Expected Value (EV) CalculatorWhat a bet is worth on average, given a price and your own probability.
• Fair Odds CalculatorTurn a probability into the price that pays it with no margin, and back again.
• Kelly Criterion CalculatorThe stake your edge justifies, at full Kelly or a safer fraction of it.
• Break-Even Win RateThe win rate a price needs before it makes you anything.