Expected goals, or xG, has changed how we understand football, and nowhere is that more visible than in the Champions League. The competition's biggest matches are now analysed through xG as much as through the scoreline, and the numbers often tell a very different story from the result. Here is how xG works in Europe's top competition, and how to use it to predict knockout form.

In simple terms, xG gives every shot a value between 0 and 1 based on how often similar shots have been scored. A penalty is worth about 0.79, a shot from inside the six-yard box might be worth 0.6, and a shot from 30 yards might be worth 0.02. Add up all the shots in a match and you get a team's total xG: a measure of the quality of the chances it created.

What the Champions League xG Numbers Say This Season

After four matchdays, the xG table tells a fascinating story. Arsenal's xG numbers are among the best in the competition, which is one reason the supercomputer makes them favourites to win the trophy. Paris Saint-Germain's numbers are also strong, reflecting their attacking quality, while Real Madrid's xG is slightly less dominant than their perfect record suggests.

The most interesting case is Liverpool. The Reds lost on Matchday 4, but their xG numbers remain strong, which is why the supercomputer still projects them to finish in the top eight. A team that creates more than it concedes will usually climb the table over time, even if individual results go against it.

xG and the Knockout Rounds

The knockout rounds are where xG becomes most valuable. In a two-legged tie, the team with the better xG over 180 minutes usually advances, even if it loses one of the legs. That is because xG measures the quality of chances created, and over two games, chance quality is a better predictor than a single result.

This is especially useful for spotting upsets. If a smaller club creates more xG than a giant in the first leg but loses 1-0, the second leg is far from over. The numbers say the underdog is creating enough to win, and the result will often catch up with the performance.

xGOT: The Missing Piece

xG measures the chance before the shot, but it does not measure the finish. That is where xGOT, or expected goals on target, comes in. xGOT re-scores the chance after the shot based on where it was placed in the goal. A tap-in that goes wide has high xG but zero xGOT. A 30-yard shot into the top corner has low xG but high xGOT.

In the Champions League this season, PSG against Arsenal produced an xG of 1.72 to 0.51, and an xGOT of 1.68 to 0.67. The two numbers together tell you that PSG created more and shot better, which is a far more complete picture than the scoreline alone.

How to Use xG to Predict Knockout Form

Look at a team's xG difference over the league phase, not just its points. A team with a strong xG difference but a modest points total is likely to improve in the knockout rounds, because its performances are better than its results. A team with a weak xG difference but a high points total is likely to regress.

Also look at xG per match, not just the total. A team that creates 2.0 xG per game is a genuine contender, whatever its league position. A team that creates 1.0 xG per game is surviving on luck or finishing, and that rarely lasts through the knockout rounds. In the Champions League, the numbers do not lie, but they do take time to tell the truth.