The away goals rule is a method of breaking ties in football matches contested over two legs in which a winner must be determined.

In many competitions, such as knockout phases of the UEFA Champions League and UEFA Cup, teams meet in two-legged "ties", defined as matches contested over two legs, one held at each contestant's home ground. The winner is determined by aggregate score over the two legs of the tie. However, in a knockout tournament, there must be a way to determine a winner if the tie is level on aggregate after the end of regular time of the second leg.

In competitions that use the away goals rule, the first tiebreaker is "away goals": the team which scored more goals on its away leg advances. As an example, let us assume a Champions League tie between Manchester United and Real Madrid, with the first leg in Manchester and the return leg in Madrid.

First leg:

• Man U 3–1 Real Madrid

Second leg:

• Real Madrid 4–2 Man U

At the end of our tie, the two teams are level 5–5 on goals. Under UEFA rules, the first tiebreaker is away goals. Real scored one goal in Manchester, but Man U scored two goals in Madrid; therefore, Man U would lead 2–1 on away goals, thereby advancing to the next round.

If a tie is level on away goals, it then goes to extra time. If after extra time the teams are level on goals, the away goals rule applies again. If the tie is still level on away goals after extra time, a penalty shootout decides which team advances.

It is sometimes stated, even by a few football commentators, that away goals are "worth double". This is not true; an away goal is identical in value to a home goal, and only becomes an issue if the tie finishes level on aggregate.

Please note that not all competitions use the away goals rule. For example, before 2005, CONMEBOL used neither the away goals rule nor extra time in any of its competitions, such as the Copa Libertadores. Ties that were level on aggregate went to an immediate penalty shootout. In 2005, CONMEBOL introduced away goals to the Copa Libertadores.

There has been at least one case of a wrong application of the away goals rule by a referee in an international club tournament. It happened during the second-round tie in the 1971-72 Cup Winners' Cup between Rangers and Sporting Lisbon.

This Rangers-Sporting tie had the following scorelines:

First leg:

• Rangers 3–2 Sporting

Second leg, after regulation:

• Sporting 3–2 Rangers

Second leg, after extra time:

• Sporting 4–3 Rangers

Since the teams were now level 6–6 on aggregate, the referee ordered a penalty shootout, which Sporting won 3–0. However, Rangers appealed the loss on the grounds that the referee should not have ordered the shootout since the Rangers' goal in extra time in Lisbon gave them a 3–2 lead on away goals. Rangers won the appeal and went on to win the Cup Winners' Cup that season.