Beginner’s guide: Effective field goal percentage and true shooting percentage

December 31, 2016 by J.H. Yeh

In a traditional box scores, the field goal made and field goal attempts can be overrated because those statistics merely tell the quantity of shots attempted and made as well as the percentage of the overall field goal percentage (FG%), 2-point field goal percentage (2FG%), 3-point field goal percentage (3FG%), and free throw percentage (FT%) on individual basis.

Players score points through a variety of ways and it can be unfair for certain types of players if we only strictly look at the field goal percentage. For player like Tyson Chandler, who makes almost all of his points around the basket and has never made a 3-point field goal before, has an impressive career field goal percentage of 59.3%. On the other hand, perimeter shooters like J.J. Redick, who averages 1.8 made 3-pointers for his career and 2.6 the last three seasons, is shooting collectively a rather unimpressive 44.8%. However, thanks to effective field goal percentage, Redick’s shooting 58.0% this season and 55.1% overall. Effective field goal percentage (eFG%) is a metric that tells the whole story on how points  adjust for the fact that 3-point field goals are worth 50%  (2 x (1+0.5) = 3)  more than 2-point field goals due to the 3-pointer’s added value. If a player never attempts a 3-point field goal, then his eFG% is the same as his FG%. The formula for eFG% is:

eFG% = (FGM + (0.5 x 3PTM)) / FGA

Below is a table of the top 15 players in eFG%. This information is as of December 31, 2016.

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The next metric is the true shooting percentage (TS%). TS% is more advanced than eFG% because it takes into account of field goals, 3-point field goals, and free throws. TS% adjusts the fact not every made shots produced in the FG% is equal. We use true shooting attempts (TSA) to calculate TS%. The formula for TSA is

TSA = FGA + (0.44 x FTA)

We use 0.44 as an approximation for the number of shots attempted each time a player is sent to the charity strpe since players go to the free throw line to shoot anywhere between one to three free throws. If players only shoot just two free throws each time, then we would use 0.5 as the approximation; however, that’s not the case. The formula for TS% is

TS% = Pts / (2 x TSA)

or

TS% = Pts / (2 x (FGA + (0.44 x FTA)))

Note that the Pts is the points the player has scored in the game. This is not the team’s score. Also note that made field goals are not included in the formula when calculating TS%, unlike eFG% and the traditional FG%. Instead, we use the player’s total points, divided by the total field goal attempts and the adjusted free throw attempts, to find out the overall efficiency of a player’s shooting. For example, on the December 29 Cavaliers vs. Celtics game, Jae Crowder had 13 points and he achieved that by attempting just nine field goal attempts and two free throw attempts. Let’s plug in the numbers to calculate his TS%

13/2*(9+(0.44*2))) = 64.22%

Crowder’s TS% for that night’s game is 64.22%. This is a very efficient percentage and certainly an efficient night for Crowder. In fact, Crowder has always been a consistently efficient player which makes him a valuable role player throughout his career. Not to mention his ability to play tough defense!

Below is the top 15 leaders in TS% in 2016-17 season.

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–J.H. Yeh

(all graphs are created by me, and all sources of information are courtesy of NBA.com and BasketballReference.com as of December 31, 2016)

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