Expected goals (xG) explained for bettors
What expected goals measures, how a 0.1 xG chance and a 0.79 xG penalty add up, and what xG can and cannot tell you about the next match price.
On this page
Expected goals, or xG, measures how good a team's chances were rather than how many it scored. Every shot gets a value between 0 and 1: the share of similar shots in the past that went in. Add a team's shots together and you get its xG for the match. For a bettor it is useful as a long-run guide to how well a side creates and concedes chances, and weak as a forecast of any single game.
How a shot gets its number
Opta, one of the main data providers, trains its model on nearly one million past shots and weighs more than 20 factors, per Opta Analyst. The biggest are:
- distance and angle to goal;
- where the goalkeeper is, and whether they can reach the shot;
- how clear the path to goal is and how much pressure the shooter is under;
- the type of shot (foot, header, volley) and how the chance was made.
A chance valued at 0.1 is scored about one time in ten. Penalties get a fixed 0.79, their historical conversion rate.
A worked example
Here is a made-up match, to show the arithmetic only.
| Chance | xG |
|---|---|
| Shot from the edge of the box | 0.05 |
| Header from a corner | 0.10 |
| Shot from inside the box | 0.15 |
| Penalty | 0.79 |
| Total | 1.09 |
That side "should" have scored about one goal. If it scored three, the finishing was well above what the chances usually produce; if it scored none, well below. Neither tells you much from one match. Over 20 or 30 games, the gap between goals and xG tends to shrink.
xG versus shots
Raw shot counts treat every attempt as equal. Liverpool had 17 shots and none on target in their 0–1 defeat to Arsenal on 1 November, per Sky Sports. A shot count makes that look like pressure; an xG figure would tell you how many of those 17 were real chances. That is the gap xG closes.
Turning xG into a betting view
xG is a description of past chances, not a price. To bet with it you still have to turn a view into a chance for each outcome, compare that with the price on offer, and only act when your chance is higher than the price implies. That last step is what expected value in betting covers, and how a full match model fits together is in how to bet on football with a model.
What this does not tell you
xG says nothing about who plays next week, the weather, a new coach or a red card. Different providers use different models, so the same match can have different xG totals. And because the market watches xG too, a team's xG story is often already in its price.
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Common questions
What is expected goals (xG) in football?
A measure of chance quality. Each shot gets a value between 0 and 1, the share of similar shots in the past that went in. A 0.1 xG chance is scored about one time in ten, per Opta's definition.
What is the xG of a penalty?
Opta gives every penalty a fixed value of 0.79 xG, its historical conversion rate.
How do I use xG for betting?
As one input on how well a team creates and concedes chances over many games, not as a forecast of one match. A team scoring far above its xG over a few games is often riding finishing that may not last, but a match price also reflects injuries, line-ups and the opponent.
Does BAI8 publish xG?
No. The BAI8 Desk publishes a chance for each outcome, a fair price and the best price it saw. This piece is about reading xG figures you see elsewhere.