# On-Base Percentage Calculator & Formula

A player's on-base percentage or on-base average, OBP, is an indicator of how often a player reaches base per plate appearance. It does not count events such as a fielding errors, fielder's choice, dropped third strikes, fielder's obstruction, catcher's interference, or sacrifice hits.

### Formula for OBP

On-base percentage is not actually a percent but a number between 0 and 1. The equation isOBP =

(H + BB + HBP)/(AB + BB + HBP + SF).

It is interesting to compare this number to a player's batting average, BA, given by the simpler formula

BA = H/AB

Rarely a player may have a lower OBP than BA. The mathematical condition for OBP to be less than BA is

(AB - H)(BB + HBP) < (H)(SF)

In other words, a player must have almost no walks or hits by pitch and a relatively high humber of sacrifice flies. This occured in 1982 with pitcher Philip Niekro. He had a total of 87 at-bats, 17 hits, 0 bases on balls, 0 hits by pitch, and 1 sacrifice fly. His OBP and BA were

OBP = (17 + 0 + 0)/(87 + 0 + 0 + 1) = 17/88 =

**0.1932**

BA = 17/87 =

**0.1954**

Sabermetricians often add the OBP and SLG (slugging percentage) to create a unified statistic called

*on-base plus slugging*, OPS.

© *Had2Know 2010
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