On-Base Percentage Calculator
On-base percentage (OBP) measures how often a batter reaches base safely, and it is one of the most valued numbers in modern baseball analysis because avoiding outs is the single scarcest resource a team has. Unlike batting average, which only counts hits, OBP credits a hitter for every way of reaching base that is within their control: a hit, a walk, or being hit by a pitch. The formula adds those three together and divides by the plate appearances that could produce an on-base outcome, namely at-bats, walks, hit-by-pitch and sacrifice flies. Sacrifice bunts are excluded by convention, while sacrifice flies are included in the denominator. The result is a decimal usually shown to three places, where about .340 is league average, .360 is good and .400 or higher is excellent. This calculator applies the standard formula exactly: enter the five inputs and it returns OBP along with the numerator and denominator so you can see how the figure is built. It is useful for comparing hitters, sanity-checking a stat line, or understanding why a patient batter who walks often rates so highly. Every figure here is computed deterministically from the formula shown below, with a worked example that reconciles exactly to the calculator.
On-base percentage is times reached base over chances to reach base: OBP = (H + BB + HBP) / (AB + BB + HBP + SF). With 150 hits, 50 walks, 5 hit-by-pitch, 500 at-bats and 5 sacrifice flies, OBP is .366.
On-base percentage formula
OBP = (H + BB + HBP) / (AB + BB + HBP + SF)
H = hits, BB = walks (bases on balls)
HBP = hit by pitch, AB = at-bats
SF = sacrifice flies
The numerator counts every way of reaching base that the batter controls, and the denominator counts the plate appearances that could have produced an on-base result.
Worked example
A hitter has 150 hits, 50 walks, 5 hit-by-pitch, 500 at-bats and 5 sacrifice flies.
- Numerator: 150 + 50 + 5 = 205 times on base.
- Denominator: 500 + 50 + 5 + 5 = 560 plate appearances.
- OBP = 205 / 560 = 0.366.
The on-base percentage is .366. These are the calculator's default inputs, so the result above matches the widget exactly.
On-base percentage calculator: frequently asked questions
What is on-base percentage (OBP)?
On-base percentage is the share of plate appearances in which a batter reaches base by a hit, a walk or being hit by a pitch. It is one of the most important batting statistics because it measures how often a hitter avoids making an out, which is the scarcest resource in baseball. An OBP around .340 is roughly average and .400 or higher is excellent.
How is OBP calculated?
OBP is the sum of hits, walks and hit-by-pitch, divided by the sum of at-bats, walks, hit-by-pitch and sacrifice flies. The denominator counts the plate appearances that can produce an on-base outcome. Sacrifice bunts are deliberately excluded from the denominator, while sacrifice flies are included.
Why are sacrifice flies in the denominator but not sacrifice bunts?
By long-standing convention the official OBP formula includes sacrifice flies in the denominator because a fly out that scores a runner still used up a plate appearance the batter did not reach base on. Sacrifice bunts are excluded, reflecting the view that a bunt is a deliberate strategic give-up rather than a failure to reach base.
How is OBP different from batting average?
Batting average is hits divided by at-bats and ignores walks entirely. On-base percentage adds walks and hit-by-pitch to the numerator and uses a wider denominator, so it captures a hitter's full ability to reach base, not just to get hits. A patient hitter who draws many walks can have a far higher OBP than batting average.
What is a good OBP?
Roughly speaking, an OBP of .340 is around league average, .360 is good, and .400 or above is excellent and usually reserved for elite hitters. Because league offensive levels change over time, OBP is most meaningful when compared against the same season's league average.
Official sources
- Public health and sport participation context: US Centers for Disease Control and Prevention (CDC). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.