Approximate Value (AV) is a metric created by Pro Football Reference founder Doug Drinen that attempts to assign a single number to a player's seasonal value, regardless of position, going back to 1960. AV works as a rough comparison tool rather than a precise measurement. AV is best thought of as an improvement on blunt measures like "number of seasons as a starter" or "number of Pro Bowl appearances."  It captures the same general idea but with more nuance in between. Because football box scores capture far less of a player's true contribution than those in baseball or basketball, AV is most reliable when comparing large groups of players rather than making fine-grained individual distinctions. A difference of two or three AV points between players in the same season shouldn't be treated as a definitive verdict on who was better.

A full breakdown of the AV formula can be found in this blog post.

At the top of every player's page on Pro Football Reference, you'll see a Weighted Career AV figure along with their ranking among all players since 1960. This is calculated by taking a declining weighted sum of a player's seasonal AV scores:

100% of their best season

95% of their 2nd-best season

90% of their 3rd-best season

85% of their 4th-best season, and so on

This weighting balances peak performance against career longevity, so that a player with several dominant seasons isn't overshadowed purely by a player who accumulated value over a very long career. Weighted Career AV is distinct from Career AV, which is simply the unweighted total of all seasonal AV scores.

On many player pages you'll find a Similar Players table, which uses AV career arcs to identify comparable players. The method starts each pair of players at 100 similarity points, then subtracts points based on differences in their AV scores season by season, with the best seasons weighted most heavily, mirroring the Weighted Career AV formula. The result surfaces players whose careers were similar in both quality and shape over time.