How this instrument works
FIP (Fielding Independent Pitching) is a sabermetric stat designed to isolate what a pitcher directly controls — home runs, walks, hit-by-pitches, and strikeouts — from what fielders and batted-ball luck control. Traditional ERA counts every earned run regardless of whether a routine grounder was booted by a fielder or a diving catch robbed a sure hit, both of which are largely outside a pitcher's control. FIP instead only weighs the 'three true outcomes' plus hit-by-pitches, scaled to look and read on the same numeric scale as ERA.
The formula, published and maintained by FanGraphs, is (13×HR + 3×(BB+HBP) − 2×K) ÷ IP, plus a FIP constant. That constant exists purely so FIP lines up with the league-average ERA in a given season — it's recalculated each year (typically landing somewhere around 3.10-3.20) so that league-average FIP always equals league-average ERA, making individual FIP values directly comparable to the ERA scale fans already know.
FIP tends to track a pitcher's true skill more consistently than ERA from year to year, since it strips out the noise of team defense quality and sequencing luck (how batted balls happen to be distributed across innings). It's not a complete picture on its own — it doesn't account for the quality of contact allowed or park factors — but it's widely used alongside ERA as a way to separate a pitcher's own performance from their defense's.
- Enter Home runs allowed (HR), Walks (BB), and Hit by pitch (HBP) for the pitcher's season or sample.
- Enter Strikeouts (K) and Innings pitched (IP).
- Adjust the FIP constant if you want a specific season's exact value — the default of 3.10 is a representative typical figure.
- Read FIP — the resulting fielding-independent pitching value, on the same scale as ERA.
- Compare the FIP result to the pitcher's actual ERA — a lower FIP than ERA often suggests bad luck or weak defensive support, and vice versa.
Worked example — a starting pitcher's full season line
Enter 15 home runs, 40 walks, 5 hit-by-pitches, 150 strikeouts, and 180 innings pitched, with the default FIP constant of 3.10. The numerator is (13x15) + 3x(40+5) − (2x150) = 195 + 135 − 300 = 30. Dividing by 180 innings gives 30/180 = 0.167, and adding the 3.10 constant lands at a FIP of 3.267.
That 3.27 FIP describes solid, above-average starting pitching — meaningfully better than a league-average FIP (which sits near the constant itself, around 3.10-3.20, by design). For comparison, a strikeout-heavy pitcher allowing just 10 HR, 30 BB, 3 HBP, and 220 K over 210 IP computes a much lower FIP of 2.045 — the high strikeout total (each K subtracts 2 in the numerator) is what drives the number down into elite territory, illustrating how heavily FIP weights missing bats over other outcomes.
Questions
Why does FIP ignore hits and balls in play entirely?
FIP is deliberately built around outcomes a pitcher controls largely independent of their fielders — home runs (which clear the fence regardless of defense), walks and hit-by-pitches (which never involve a fielder), and strikeouts (which end the at-bat with no ball in play). Whether a routine grounder becomes an out or a hit depends heavily on defensive positioning and fielder skill, which is exactly what FIP is designed to exclude, so it treats all non-home-run, non-strikeout balls in play as noise rather than pitcher skill.
What does the FIP constant actually do, and why isn't it just zero?
Without an added constant, the raw (13xHR + 3x(BB+HBP) − 2xK)/IP calculation would produce numbers on an arbitrary scale that don't resemble ERA at all. The FIP constant is calculated each season specifically so that league-average FIP equals league-average ERA that year, making individual FIP values directly comparable to the ERA numbers fans are already used to reading. It typically lands around 3.10-3.20 depending on the season's overall run-scoring environment.
What counts as a 'good' FIP?
Since FIP is scaled to match ERA, the same rough intuition applies: below 3.00 is excellent, 3.00-3.75 is solidly above average, roughly 3.75-4.50 is close to league average, and above 4.50 generally signals below-average performance in most run-scoring environments. Because the FIP constant shifts slightly year to year with the league's overall offensive levels, exact cutoffs move a bit season to season, but the ERA-like scale keeps the general reading points consistent.
How is FIP different from xFIP or SIERA?
FIP uses only actual home runs allowed; xFIP is a variant that instead estimates 'expected' home runs from a pitcher's fly-ball rate and the league-average home-run-per-fly-ball rate, smoothing out year-to-year home run luck (which can be influenced by park factors and short-term variance). SIERA goes further, incorporating batted-ball profile (ground balls vs. fly balls vs. line drives) alongside the FIP-style core inputs. FIP remains the simplest and most widely reported of the three, and the one this calculator computes.
Can I use partial-season or single-game stats in this calculator?
Yes — the formula works identically at any sample size, since it's just a ratio of counting stats to innings pitched. Keep in mind that FIP (like most rate stats) is noisier over small samples — a single start or a few innings can swing wildly based on a couple of home runs or strikeouts — so it's most meaningful as a season-length or multi-start sample rather than a tiny handful of innings.