OBP Calculator

520 at-bats, 165 hits, 55 walks, 4 hit-by-pitch and 5 sac flies give an OBP of .384

On-base percentage (OBP) is how often a batter reaches base without making an out. Official Baseball Rule 9.21(f) says to add hits, walks and hit-by-pitch, then divide by the sum of at-bats, walks, hit-by-pitch and sacrifice flies. For the line above, the numerator is 165 + 55 + 4 = 224, the denominator is 520 + 55 + 4 + 5 = 584, and 224 ÷ 584 = 0.3835…, which rounds to .384 at three decimals. Per 100 plate appearances, that is 38.4 times on base.

.384 is .066 above the 2026 MLB regular-season league average of .318. Even so, 6 of the 135 other qualified MLB hitters were higher. The league average includes pinch hitters and bench players, while qualified hitters are the regulars. The calculator above shows both comparisons side by side. The fields follow the official fraction, with the numerator on top and the denominator below, and walks and hit-by-pitch are entered once in the top row and mirrored in the denominator.

Why look at on-base percentage

A team gets only 27 outs in a game. FanGraphs describes OBP as measuring "the most important thing a batter can do at the plate: not make an out," and says it captures contributions to run scoring better than batting average because it includes walks, which batting average ignores. A hitter at .260 who walks a lot and a hitter at .290 who almost never walks can end up with similar OBPs. That is why OBP comes first in situations like these.

• Choosing a leadoff or No. 2 hitter: These hitters need to be on base when the middle of the order comes up. For these spots, look at OBP before batting average.
• Checking plate discipline: A big gap between OBP and batting average means a large share of trips to first came on walks and hit-by-pitch. Among 2026 MLB qualified hitters, Mike Trout (LAA) had the biggest gap, with a .242 batting average and a .382 OBP.
• Rec leagues and youth/high-school ball: With at-bats, hits and walks from the scorebook, you can add up the games and calculate right away. Enter totals like 4+3+5 in each field and the calculator divides the sums.
• Reading OPS and wOBA: OPS is OBP plus slugging percentage, and wOBA is a "weighted on-base average" that gives each way of reaching base its own run value. Knowing OBP shows what those two stats build on.

How to use it

1. Pick a league to compare with. Tap KBO, MLB or NPB. The league average, the dotted outline on the 100-PA board and the dots in the ranking below all switch to that league's 2026 regular season.
2. Enter hits, walks and hit-by-pitch in the numerator. Walks (BB) already include intentional walks. Walks and hit-by-pitch are mirrored in the denominator, so do not enter them again. Blank fields count as 0.
3. Enter at-bats and sac flies in the denominator. Use at-bats (AB), not plate appearances (PA). Sacrifice bunts do not go in anywhere.
4. Read the result. The 100-PA board scales your line down to 100 plate appearances and colors it by hits, walks, hit-by-pitch, outs and sac flies. The dotted outline is where the average hitter in that league gets on base. The verdict sentences compare your line with the league average, the qualified hitters and the way of reaching base, in that order.
5. Try a target OBP. If the target is above your OBP, you see how many plate appearances in a row you would need to reach base to get there. If it is below, you see how many outs in a row you could make and still stay above it. Copy result and Copy link share the current line as it is.

How OBP is calculated

• OBP = (hits + walks + hit-by-pitch) ÷ (at-bats + walks + hit-by-pitch + sacrifice flies)
• Batting average = hits ÷ at-bats (walks, hit-by-pitch and sac flies are not at-bats)
• Times on base per 100 PA = OBP × 100

The KBO records site and MLB's official stats both give OBP to three decimals. Baseball stats usually drop the leading zero and write .384, and 1.000 means the batter reached base in every plate appearance.

What goes in the numerator and denominator, and what stays out

For several games, divide the totals

A season OBP is not the average of single-game OBPs. Games have different numbers of plate appearances, so add up hits, walks, hit-by-pitch, at-bats and sac flies separately and divide once.

If you enter at-bats as 1+4, hits as 1+0 and walks as 0+1, the calculator uses the totals, and the formula line ends with "sum of 2 games".

League average OBP (2025 and 2026 regular seasons)

These values add up every team's hitters in the league. Pitchers still bat in the NPB Central League in 2026, so Central League pitcher batting is left out.

In 2026 the KBO had the highest OBP of the three leagues, up from .338 in 2025 to .346. MLB also edged up from .315 to .318. Per 100 plate appearances, the average KBO hitter gets on base 34.6 times, the average MLB hitter 31.8 times and the average NPB hitter 30.9 times. So a .330 OBP is below average in the KBO but above average in MLB and NPB. Walks and hit-by-pitch made up 32% of times on base in both the KBO and MLB, and 29% in the NPB.

Looking only at qualified hitters raises the bar

A qualified hitter needs 3.1 plate appearances per team game (Official Baseball Rule 9.22(a)). In 2026 only one of the 135 qualified MLB hitters topped .400, Yordan Alvarez, and the runner-up, TJ Rumfield (COL), was at .390. In the KBO, 8 of 49 qualified hitters topped .400, led by Koo Ja Wook at .458. In the NPB, Kensuke Kondo was the only one over .400.

The same OBP can come from very different ways of getting on base

OBP adds the share of trips to first from hits and the share from walks and hit-by-pitch. Two hitters with nearly the same OBP can therefore get on base in completely different ways. Below are the pairs of 2026 qualified hitters whose OBP differs by .003 or less and whose ways of reaching base differ the most.

Munetaka Murakami and Luis Arraez are .002 apart in OBP but .103 apart in batting average. More than half of Murakami's times on base were walks or hit-by-pitch, while Arraez got on base by a hit 83% of the time. On the 100-PA board, Murakami's pale walk cells cover far more of the grid. In the KBO, Kim Jae Hwan and Park Jae Hyun show the same pattern: .002 apart in OBP, .076 apart in batting average, with 45% of Kim's times on base coming from walks and hit-by-pitch against 17% for Park.

What counts as a good OBP

The FanGraphs scale was made in 2010 with MLB in mind. The 2026 MLB average of .318 is close to the scale's "Average" mark of .320, but the 2026 KBO average of .346 is above even "Above Average" at .340. All 49 KBO qualified hitters cleared .310, and 11 reached .390, the "Excellent" mark. For KBO lines, compare with the league average and the qualified median instead of this scale. The reading row in the calculator shows where your OBP falls on the scale as "between two marks".

The highest OBPs of all time

Bonds reached base 376 times in 617 plate appearances in 2004. He drew 232 walks, 120 of them intentional. His .362 batting average was high too, but 62% of his times on base were walks. Baseball-Reference also lists Negro leagues records, which is why Josh Gibson, Charlie Smith and Oscar Charleston appear (the site notes that Negro leagues data is incomplete). Tap the "Bonds 2004" example in the calculator and this line fills 61 cells of the 100-PA board.

Common mistakes

• Putting sacrifice bunts in the denominator: Sacrifice bunts come out of both the numerator and the denominator. Adding them lowers the OBP.
• Leaving out sac flies: Sac flies go in the denominator. Dropping them inflates the OBP. In the example above, dropping the 5 sac flies gives 224 ÷ 579 = .387.
• Counting reaching on an error as being on base: Reaching on an error, fielder's choice or dropped third strike counts as an at-bat only, not as a time on base.
• Dividing by plate appearances (PA): Plate appearances include sacrifice bunts and catcher's interference, so they are not exactly the denominator. FanGraphs says the swap usually makes little difference but is not perfectly equivalent.
• Averaging single-game OBPs: That weights games with few and many plate appearances equally. Add up the stats first, then divide.
• Adding intentional walks a second time: Walks (BB) in a stat table already include intentional walks (IBB).

Limits

• OBP counts a home run and an infield single as the same single time on base. That is why FanGraphs says to use it alongside other stats. To see power too, look at OPS or wOBA.
• Stolen bases, baserunning and defense are not included. What a runner does after reaching base needs other stats.
• There is no park, league or season adjustment. In 2026 alone the league averages are .346 in the KBO and .309 in the NPB, so comparing OBPs across leagues as they are is easy to get wrong.
• Small samples swing a lot. FanGraphs puts the point where a hitter's OBP stabilizes at 460 plate appearances (based on Russell Carleton's work).
• The FanGraphs scale is for MLB and dates from 2010. For the KBO and NPB, start with the league average and the qualified median.
• The NPB 2026 league totals were rebuilt because the official site (npb.jp) could not be reached: Sportsnavi team player stats plus the stats of players who changed teams mid-season were added up. Compared with the team pitching totals, the rebuilt totals are short by 31 plate appearances, 6 hits and 1 walk, and hit-by-pitch matches. The NPB 2025 average is not shown because Central League pitcher batting totals were not available.

As of The formula and explanations were checked on 2026-10-23 against the Official Baseball Rules 2026, the MLB Glossary, the FanGraphs Library and Baseball-Reference. League averages and qualified hitters were calculated from the final 2026 regular-season records and the 2025 regular-season records downloaded on 2026-10-22 from the KBO Records site, MLB's official stats (Stats API) and NPB records.

Sources

• 01Official Baseball Rules 2026 Edition9.21(f) OBP definition and comment (first base on interference, obstruction or shift-restriction violation is ignored), 9.22(a) qualifying PA (team games × 3.1), 9.02(a)(1) cases not charged as an at-bat
• 02MLB Glossary — On-base Percentage (OBP)Errors, fielder's choices and dropped third strikes do not count; why sacrifice bunts are removed from the formula
• 03FanGraphs Library — OBPPiper Slowinski (2010-02-16): not making an out, the .290 to .390 scale, every time on base weighted equally, PA as denominator is not exactly equivalent
• 04FanGraphs Library — Sample SizeHitter OBP stabilizes at 460 PA, per Russell Carleton
• 05KBO Records — Team stats (hitters)2026 and 2025 regular-season totals for the 10 teams (match the league OBPs of .346 and .338)
• 06KBO Records — Player stats (hitters)AB, H, BB, HBP and SF of the 49 qualified hitters in 2026 (match the OBPs in the tables)
• 07MLB Stats API — 2026 team hitting statsTotals for the 30 teams; 2025 uses season=2025; the 135 qualified hitters come from the qualified list of the same API
• 08NPB — 2026 Central League qualified hitters (archived)Together with the Pacific League table (bat_p), 45 qualified hitters; archived 2026-10-08
• 09Sportsnavi (Yahoo! JAPAN) — NPB standings and club batting pagesFrom the standings, each of the 12 clubs links to a batting page (teams/…/battingstats). League totals rebuilt by adding up the 2026 player stats of the 12 NPB teams
• 10Baseball-Reference — Single-Season Leaders for On-Base %Ranks 1 to 5 (checked 2026-10-23); recent seasons require 3.1 PA per team game
• 11Baseball-Reference — Career Leaders for On-Base %Ranks 1 to 5; career rate stats require 3,000 PA or more
• 12MLB Stats API — Barry Bonds year-by-year hitting2004: 373 AB, 135 H, 232 BB (120 intentional), 9 HBP, 3 SF (the "Bonds 2004" example)

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