FIP Calculator — Fielding Independent Pitching, With Real League Constants

Background.

FIP — fielding independent pitching — asks what a pitcher's ERA would have been if everything outside his control had gone exactly averagely. The FanGraphs Sabermetrics Library, which publishes the canonical definition, puts it as measuring "what a player's ERA would look like over a given period of time if the pitcher were to have experienced league average results on balls in play and league average timing". MLB's own glossary says the same thing more bluntly: FIP "focuses solely on the events a pitcher has the most control over — strikeouts, walks, hit-by-pitches and home runs" and "entirely removes results on balls hit into the field of play".

The idea traces to research by Voros McCracken in the early 2000s, which found that the rate at which balls in play fall in for hits against a given pitcher barely correlates from one season to the next. If a pitcher cannot repeat it, it is mostly defence, park and luck — and a statistic that wants to describe the pitcher should throw it out. What is left is the three-true-outcome core: the home runs he gave up, the men he put on without a ball being fielded, and the batters he retired without help.

The formula both sources publish is (13×HR + 3×(BB+HBP) − 2×K) ÷ IP, plus a constant. The weights are not arbitrary: they approximate the run value of each event, which is why a home run at 13 is worth more than four walks and a strikeout at −2 is worth about a sixth of a home run. The constant does no analytical work at all — its only job is to slide the result onto the ERA scale, so that a league-average pitcher's FIP equals the league's actual ERA. That means the constant is specific to a league and a season, and using the wrong one silently shifts every answer.

This calculator does not guess the constant. It stores the official season pitching totals for all thirty Major League clubs — earned runs, outs, home runs, walks, hit batsmen and strikeouts — for 2023, 2024 and 2025, and recomputes the constant from the published definition at full precision every time you press the button. That derivation is checkable in two ways, and both are held as unit tests. The league ERAs it implies (4.33, 4.07 and 4.15) match the league ERAs Major League Baseball publishes for those seasons. And feeding a season's own league line back into the calculator as though it were a pitcher returns a FIP exactly equal to that season's league ERA, which is precisely what "the constant puts FIP on the ERA scale" is supposed to mean.

One honest caveat, stated here rather than buried. Published FIP figures for the same pitcher differ slightly between sources, because every publisher derives its own constant from its own league aggregation and its own choices about which innings to include. Differences of a few hundredths are normal and do not indicate an error in either calculation. What this page guarantees is that the formula is the published one, the constant is derived transparently from official league data you can re-query yourself, and both the constant and the raw rate are shown as separate outputs so you can see exactly how the answer was assembled.

Below the widget you will find the formula with both source citations, the constant derivation worked through arithmetically, a worked example reproducing a Cy Young season from official MLB data across all three league scales, and an account of what FIP still misses — chiefly that it credits a pitcher with no control at all over the quality of contact, which the batted-ball tracking era has shown to be an overstatement.

What is fip calculator?

FIP (fielding independent pitching) is an estimator of a pitcher's run prevention built only from the outcomes that involve no fielder: home runs, walks, hit batsmen and strikeouts. Its formula, published identically by FanGraphs and by MLB's official glossary, is (13×HR + 3×(BB+HBP) − 2×K) ÷ innings pitched, plus a league constant that puts the result on the ERA scale. It is not an official statistic and appears nowhere in the Official Baseball Rules. Because it is scaled to ERA, it is read the same way: for the run environments of the last few seasons, roughly 4.10 to 4.20 is around average, under 3.50 is very good and under 3.00 is elite. FanGraphs publishes a rules-of-thumb table — Excellent 3.20, Great 3.50, Above Average 3.80, Average 4.20, Below Average 4.40, Poor 4.70, Awful 5.00 — explicitly labelled as being based on the 2016 run environment, so it should be shifted for the season you are looking at. FIP's main use is diagnostic: a pitcher whose ERA sits well below his FIP has usually been helped by defence, sequencing or a low home-run-per-fly-ball rate, and the two figures tend to converge over time. Its main limitation is that treating all balls in play as equal understates the real, if modest, control pitchers have over contact quality — which is why expected-run estimators built on batted-ball tracking now sit alongside it rather than being replaced by it.

How to use this calculator.

1. 01Choose the league scale first. The constant differs by season — 3.249 for 2023, 3.160 for 2024, 3.128 for 2025 — and using the wrong one shifts the answer by up to a tenth of a run.
2. 02Enter home runs allowed, walks allowed, batters hit by a pitch and strikeouts. All four come straight from a standard pitching line, and hit batsmen are genuinely part of FIP even though WHIP excludes them.
3. 03Enter innings pitched in baseball notation. 192.0 is 192 innings; 177.2 is 177 and two thirds. Check the true-decimal output before reading anything else.
4. 04For a league that is not pre-loaded, choose Custom and enter that league's own constant, computed as its league ERA minus its league fielding-independent rate. Do not reuse an MLB constant for an amateur league — the run environments are nothing alike.
5. 05Read the three components against each other. A negative fielding-independent rate is normal for a strikeout pitcher and simply means the strikeout term outweighs the other two.
6. 06Compare the result against the pitcher's actual ERA for the same period. A gap in either direction is the interesting part; the two numbers agreeing tells you very little.

The formula.

There are two halves: the rate, which describes the pitcher, and the constant, which describes the league.

The rate. Multiply home runs by 13, walks plus hit batsmen by 3, strikeouts by 2. Add the first two, subtract the third, divide by innings pitched. For a line of 15 home runs, 35 walks, 9 hit batsmen and 228 strikeouts in 192 innings: 195 + 132 − 456 = −129, and −129 ÷ 192 = −0.671875. A negative rate is completely normal and simply means the strikeouts outweighed the damage; it is not an error and it is not a negative FIP, because the constant has not been added yet.

The constant. FanGraphs defines it as lgERA minus the league's own fielding-independent rate. Work it for 2024 from the official league totals: 129,349 outs is 43,116.33 innings, and 19,508 earned runs over that gives a league ERA of 9 × 19,508 ÷ 43,116.33 = 4.0721. The league's own raw rate is (13×5,453 + 3×(14,929 + 2,020) − 2×41,197) ÷ 43,116.33 = 39,342 ÷ 43,116.33 = 0.9125. Subtract: 4.0721 − 0.9125 = 3.1596. That is the 2024 constant, and it is derived rather than copied — this calculator stores the six league totals and redoes the division at full precision every time, so no rounding is baked in.

Add them: −0.671875 + 3.1596 = 2.4877, printed 2.49.

Why the constant has to be season-specific: it is defined so that a league-average pitcher lands on the league's actual ERA. Change the season and both terms of the subtraction move — 2023 had more offence, a league ERA of 4.33 and a constant of 3.249; 2025 had a constant of 3.128. The same raw pitching line therefore reads 2.577 on the 2023 scale and 2.456 on the 2025 scale. That spread of 0.12 runs is larger than the gap between a good starter and a very good one, which is why the dropdown matters.

The innings denominator follows the same rule as ERA. Official Baseball Rule 9.02(c)(1) counts each putout as one third of an inning, so the box-score figure is whole innings followed by a digit counting leftover outs. Convert to outs, then divide by three. A fractional part of .3 or higher is impossible and is rejected rather than silently coerced.

One thing this page deliberately does not offer is xFIP, which replaces a pitcher's actual home runs with an expected total derived from his fly balls and a league home-run-per-fly-ball rate. That requires a second league constant this page cannot source from official data, so rather than guess it, xFIP is left out.

A worked example.

Frequently asked questions.

References& sources.

1. [1]FanGraphs Sabermetrics Library, "FIP". Source of the formula "FIP = ((13*HR)+(3*(BB+HBP))-(2*K))/IP + constant", of the constant's definition "FIP Constant = lgERA – (((13*lgHR)+(3*(lgBB+lgHBP))-(2*lgK))/lgIP)", of the statement that the constant "is solely to bring FIP onto an ERA scale and is generally around 3.10", of the description of FIP as league-average results on balls in play and timing, of the reference to Voros McCracken's early-2000s research, and of the rules-of-thumb table quoted here with its "Based on 2016 Run Environment" qualification.
2. [2]Major League Baseball. Official MLB Glossary, "Fielding Independent Pitching (FIP)": FIP "focuses solely on the events a pitcher has the most control over -- strikeouts, walks, hit-by-pitches and home runs" and "entirely removes results on balls hit into the field of play", with the formula "((HR x 13) + (3 x (BB + HBP)) - (2 x K)) / IP + FIP constant" where the constant "puts FIP onto the same scale as the entire league's ERA". Second independent publication of the identical formula.
3. [3]MLB Stats API (statsapi.mlb.com), club season pitching totals for all 30 clubs. Summing them gives the league aggregates from which the constants on this page are derived: 2024 — 19,508 earned runs, 129,349 outs, 5,453 home runs, 14,929 walks, 2,020 hit-by-pitch, 41,197 strikeouts, for a league ERA of 4.0721 and a FIP constant of 3.1596. The same query gives 2023 (league ERA 4.33, constant 3.249) and 2025 (4.15, 3.128); the derived league ERAs match MLB's published figures for those seasons.
4. [4]MLB Stats API (statsapi.mlb.com), season pitching statistics for player 669373 (Tarik Skubal), 2024: innings pitched "192.0", outs 576, home runs 15, walks 35, hit by pitch 9, strikeouts 228, published era "2.39". Source of the worked example on this page.
5. [5]Office of the Commissioner of Baseball (2025). Official Baseball Rules, 2025 Edition, Rule 9.02(c)(1) Comment: "In computing innings pitched, the Official Scorer shall count each putout as 1/3 of an inning." Source of the innings-notation parsing. A full-text search of the same document confirms that FIP is not defined anywhere in the official rules.