How it works
On-base percentage is how often a batter reaches base. Hits, walks and hit-by-pitches count as times on base. Reaching on an error, a fielder’s choice or a dropped third strike does not.
The bottom of the fraction is at-bats plus walks, hit-by-pitches and sacrifice flies. Sacrifice bunts are left out entirely, as are times a batter is awarded first base for interference or obstruction.
The table assumes the next four plate appearances are all at-bats, with hits as the way on base.
The formula
OBP = (hits + walks + hit by pitch) ÷ (at-bats + walks + hit by pitch + sacrifice flies)Worked example
A season of 165 hits, 60 walks and 5 hit-by-pitches in 550 at-bats, with 5 sacrifice flies.
- Times on base: 165 + 60 + 5 = 230.
- Times counted: 550 + 60 + 5 + 5 = 620.
- 230 ÷ 620 = .371, against a batting average of .300.
Questions
Why do sacrifice flies count but sacrifice bunts do not?
That is how rule 9.21(f) defines it. MLB explains that a sacrifice bunt is usually the manager’s call rather than the hitter’s, so bunts are removed from the calculation.
Does reaching on an error count?
No. Errors, fielder’s choices and dropped third strikes do not count as times on base, but the at-bat still counts, so they lower OBP.
When did OBP become official?
Branch Rickey and Allan Roth of the Dodgers devised it in the 1940s and 1950s. It became an official MLB statistic in 1984.
How many at-bats do you need to qualify for the batting title?
It is counted in plate appearances, not at-bats. Rule 9.22 sets the minimum at 3.1 plate appearances for every game on the team’s schedule: 502 in a 162-game season. A player short of that can still win if their average stays highest after the missing plate appearances are added as hitless at-bats. The same rule covers slugging and on-base percentage.
Add this calculator to your site
Team, league or blog? You can put this calculator on your own site for free. Copy the code below into your page’s HTML. The calculator updates itself whenever we improve it.
The short script lets the frame grow to fit the calculator on your page. Please keep the credit line underneath it.
Sources
- Major League Baseball. Official Baseball Rules, 2026 edition. Rule 9.02(c)(1) comment (each out is one third of an inning pitched), rule 9.21 (how to compute batting average, slugging percentage, earned run average and on-base percentage, with a worked ERA example) and rule 9.22 (minimum plate appearances and innings to qualify for a title).
- MLB.com glossary: On-base Percentage (OBP). Hits, walks and hit-by-pitches count; errors, fielder’s choices and dropped third strikes do not; sacrifice bunts are left out. Official statistic since 1984.