A betting edge is how far the price you take sits above the fair price for an outcome, written as a percentage: edge = offered price / fair price - 1. With illustrative prices, $2.52 against a fair $2.40 is 2.52 / 2.40 - 1 = 5%, so each dollar staked is worth 5 cents of profit on average, provided $2.40 really is fair.
The fair price is 1 / the outcome's true chance, which can only be estimated, so every edge is an estimate. A negative edge, which the margin builds into most bookmaker prices, loses on average however you stake it, which is why edge comes first in any betting strategy.
How to calculate your edge
Divide the price on offer by the fair price, then subtract 1. With illustrative prices:
| Price on offer | Fair price | Edge: offered / fair - 1 | True chance: 1 / fair | Chance the price implies: 1 / offered |
|---|---|---|---|---|
| $2.52 | $2.40 | +5.0% | 41.7% | 39.7% |
| $9.00 | $8.00 | +12.5% | 12.5% | 11.1% |
| $1.44 | $1.50 | -4.0% | 66.7% | 69.4% |
The $1.44 bet loses on average: its price implies 69.4% for an outcome that wins 66.7% of the time. Value betting covers where a fair price comes from.
Edge vs expected value per bet
Expected value (EV) turns an edge into dollars: EV per $1 = win chance x decimal odds - 1. When the win chance is 1 / the fair price, EV per $1 equals the edge, so EV per bet = stake x edge. A $40 bet on the illustrative $9.00 price, fair at $8.00, is worth 40 x 0.125 = $5.00 on average, the same as 0.125 x 9.00 x $40 - $40. The expected value calculator runs it for any stake.
The two part company on other kinds of bet:
- A bonus bet usually pays only its winnings (check the bookmaker's terms). A $40 bonus bet at $2.52 with a fair $2.40 is worth (1 / 2.40) x (2.52 - 1) x $40 = $25.33 on average. Its price still carries a 5% edge.
- Exchange commission comes off net winnings in a market. At $9.00 with an illustrative 6% rate, a win pays the same as a price of 1 + (9.00 - 1) x (1 - 0.06) = $8.52, an edge of 8.52 / 8.00 - 1 = 6.5%.
Risk: Betting involves risk. The $9.00 bet above loses seven times in eight, a bonus bet that loses pays nothing, and an edge measured against a wrong fair price is no edge at all. See responsible gambling for limits and support.
Edge percentage vs the gap in chances
An edge percentage is not a gap between chances. The $9.00 bet's 12.5% edge rests on 12.5% - 11.1% = 1.4 percentage points, and the $2.52 bet's 5% edge on 2.0 points (41.7% - 39.7%).
So the longer the price, the smaller the estimate error that wipes an edge out. A 5% edge at $9.00 would rest on 0.56 points: a fair price of 9.00 / 1.05 = $8.57, so a true chance of 11.67% against the 11.11% the price implies. Set a minimum edge that suits your prices.
Mistakes that misstate an edge
| Mistake | What it does |
|---|---|
| Turning the formula round | 2.40 / 2.52 - 1 = -4.8% makes a value bet look like a losing one |
| Treating another bookmaker's price as fair | If the $2.40 came from a two-way market adding up to 105%, its margin-free price is 2.40 x 1.05 = $2.52 (proportional method), and $2.52 elsewhere has no edge |
| Reading an edge as a likely result | At a 5% edge the $2.52 bet still loses about 58% of the time |
Edges on B337's +EV screener
B337's +EV screener lists bookmaker prices on sports markets that sit above a fair price, largest edge first. Each fair price comes from stripping the margin out of prices across the market, including exchanges and global market references, and you can change how it is built. The rows come with Terminal Pro and Full Automation, or a Screeners plan set up with the team; a free account sees the live counts with the rows locked.
Each bet is your decision, placed in your own bookmaker account, and bets placed through B337 use credits. The board reads prices on a repeating cycle, so a listed price can already have moved: check it with the bookmaker first.
For free and confidential support call 1800 858 858 or visit gamblinghelponline.org.au.
Risk: Betting involves risk. A screener edge is an estimate made when the prices were read. Bookmakers can limit stakes, void bets or close accounts, and many restrict automated betting in their terms. There is no guarantee of profit. See responsible gambling for limits and support.