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Expected Goals Calculation (xG)
xG is a measurement of the quality of a goalscoring chance.
When a chance is created in football it is analysed and given an xG figure.
These figures are then totalled at the end of the game to give an xG figure for the game.
The xG figures are based on data research that have measured 0000's of historical shots.
They have already calculated the percentage chance of a goal being scored from that position of play from the database, it is then given an xG figure.
If a chance was a golden opportunity and would normally be scored it receives a high (xG) figure, if it was a speculative long-range shot it would be given a much lower (xG) figure.
E.G: If a goal opportunity had an 80% chance of being scored then the xG would be measured as 0.8.
E.G: If a goal opportunity had a 30% chance of being scored then the xG would be measured as 0.3.
E.G: A penalty has a 76% chance of being scored, the xG figure is 0.76.
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The xG figure is calculated based on a range of variables including:
The distance the shot was taken from the goal.
Did the chance come from open play.
Was it a shot or a header
The angle the shot came from.
xG Example Matches
Below is an example from the 2020/21 Championship game between Wycombe and Queens Park Rangers.
| Match | Result | XG |
|---|---|---|
| Wycombe | 1 | 1.99 |
| QPR | 1 | 0.61 |
You can see that Wycombe Wanderers based on the quality of chances created were a tad unfortunate not to win the game and that QPR were fortunate to get the draw based on the range of chances created.
In that weekend of games, Wycombe had the highest XG of any home team.
You can see below how another game in the Championship that weekend panned out.
| Match | Result | XG |
|---|---|---|
| Huddersfield | 2 | 1.03 |
| Watford | 0 | 3.25 |
In this game, you can see that on the quality of chances created in the game Watford should have won.
Huddersfield's 2 goals came from a mistake by the goalkeeper and an own goal, whereas Watford had 21 goal attempts, and had the highest xG of any away team that weekend.
That result cost the Watford manager his job, but maybe the owners should have looked at the xG before taking action?
In the two examples above you can see that despite creating a lot neither side with the higher xG won the game, but a high xG could point you in the right direction when placing future bets on team, especially if that team is consistently receiving a high xG.
However, you will still need to use all your gleaned knowledge on assessing a football match when looking to strike winning bets.
Bookmakers xG
The xG figures are available from a range of websites and are published once the games are finished.
There is a range of online xG tables so you can check the previous home and away performance.
You can quickly see how a team performed in a game based on chances created, and the quality of those chances.
However, the bookmakers also have access to xG and you can expect their odds in future games to reflect recent xG measurements.
This is why it is so important to undertake more of your own research when placing a football bet.
You may consider:
- Historical XG
- Poisson Theory
- Home and Away Form
- Current Form
- Opposition Quality
- Results
- Injury News
- Players Suspended
- Quality of Bench
- League Position
- Betting Odds
- Momentum
- Historical Form
- In-Play Odds
Many OLBG tipsters already do this and you can see the most successful football tipsters via the monthly tables.
You can tip on a range of leagues and then place bets directly from OLBG at the best prices.
The OLBG forum has a dedicated xG discussion thread, please do add your thoughts and opinions on that thread.
