Aging Curves
Stat of the Week
by Peter Liubicich
Aging Curves
This post was written by Peter Liubicich on December 10, 2012
Posted Under: Stat of the Week

With Josh Hamilton being the biggest free agent still on the market, it is important that we look at Aging Curves and how teams will look at a player and manage their expectations as the player grows older.  The areas that are looked at primarily for Aging Curves for position players are a player’s hitting ability and his fielding ability.

Steve Slowinski of FanGraphs explains that the process to making an Age Curve uses the same methods used to find a Minor Leaguer’s Major League Equivalence which uses a player’s stats in the minors and tries to project what their stats will be in the majors.  According to Slownski, when looking at Aging Curves, a player usually peaks in terms of defense earliest in their career and peaks in terms of hitting in their late twenties.

Jeremy Greenhouse of Baseball Analysts also did some investigating into Aging Curves and broke down different players by their hitting abilities, calling them Good Hitters and Bad Hitters and used WAR to evaluate a player’s value over their career.  Greenhouse found that bad hitters peaked two years earlier than good hitters and that players that draw a lot of walks peak one year earlier than players that don’t draw as many walks, but also fade faster.

Bradbury in his article article he quotes Bill James’ evaluation of the aging curve for hitters:

“Good hitters stay around, weak hitters don’t. Most players are declining by age 30; all players are declining by age 33. There are difference in rates of decline, but those differences are far less significant for the assessment of future value than are the differing levels of ability (James, 1982, p. 205).”

Finally, J.C. Bradbury also did an analysis of Aging Curves over an 86 year period.  He found that the peak for hitters is around 29 years old, and possibly 30 in the modern game.  Below is a chart of the peak age for hitters through different hitting statistics:

Peak Age by Skill



Peak Age

Linear Weights








Walk Rate




Home Run Rate


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Reader Comments


  1. Aging Curves — Player Analysis  on December 14th, 2012 @ 4:36 pm
  2. Aging Curves and UZR  on December 20th, 2012 @ 4:30 pm

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