⚾ FIP Calculator

How to Use This FIP Calculator

FIP asks a simple question: how would this pitcher's ERA look with league-average defense and league-average luck on balls in play? It uses only the outcomes a pitcher truly controls: strikeouts, walks, hit batters, and home runs. Enter those five numbers plus the FIP constant, and get the pitcher's defense-free performance level.

The FIP Formula

The weights come from linear run-value research: a home run costs about 13 times a generic out, a walk about 3, and a strikeout saves about 2 relative to a ball in play. Dividing by innings and adding the constant puts FIP on the ERA scale so the numbers read familiarly. Balls in play are deliberately excluded because pitchers control them far less than strikeouts and walks; that is the whole philosophical bet of FIP. The constant changes yearly with the run environment and hovers near 3.10 in recent MLB seasons.

Worked Example

Enter 18 HR, 45 BB, 6 HBP, 180 K, 175.67 IP, constant 3.10. Numerator = 13x18 + 3x(45+6) - 2x180 = 234 + 153 - 360 = 27. Divide by 175.67 = 0.1537. Add 3.10 = 3.2537, shown as 3.25. The per-9 rates: K/9 = 180/175.67x9 = 9.22, BB/9 = 2.31, HR/9 = 0.92. A 3.25 FIP is very good, roughly a number-two starter. If this pitcher's ERA were 4.20, the gap would scream bad luck or bad defense; if ERA were 2.60, expect regression.

ERA vs FIP: Reading the Gap

ERA measures what happened, including bloops, errors, and great catches. FIP measures the pitcher's repeatable skills. Big gaps usually close over time: pitchers with FIP a run below ERA tend to improve their ERA the next season, and vice versa. But persistent gaps exist too. Extreme ground-ball pitchers can beat their FIP by inducing weak contact, knuckleballers and soft-tossers live in the gaps, and Coors Field inflates everything. Use FIP as the baseline expectation and ERA as the story of what actually happened, then look for reasons when they disagree.

Limits of FIP

FIP assumes all balls in play are luck, which is mostly but not entirely true: pitchers do influence exit velocity and launch angle somewhat. It ignores caught stealing, pickoffs, and sequencing, and it treats every home run equally whether it barely cleared the wall or left the stadium. Small samples make it noisy; 30 innings of FIP tells you little. Variants like xFIP normalize home run rate to league-average fly-ball rates, which helps young pitchers with fluky homer totals. FIP is the best single defense-free number, not the whole truth about a pitcher.

A Second Worked Example: The Unlucky Ace

Twenty-five home runs, 40 walks, 5 hit batters, 200 strikeouts, 190 innings, constant 3.10. Numerator: 13 times 25 is 325; 3 times 45 is 135; 2 times 200 is 400. Total: 325 plus 135 minus 400 is 60. Divide by 190: 0.3158. Add 3.10: 3.42 FIP. A 3.42 is solidly above average, roughly a number-two or three starter. If this pitcher's ERA sat at 4.60, the 1.18 gap screams bad defense or bad luck on balls in play, and smart teams would expect the ERA to fall toward the FIP next season.

Flip it: a 2.80 ERA with a 4.10 FIP is a pitcher living on borrowed time. The balls in play found gloves, the runners stranded at improbable rates, and the bill comes due eventually. FIP does not predict the future perfectly, but the gap is the best single indicator of which ERAs are real and which are rented.

xFIP: Normalizing the Home Runs

FIP still includes home runs, and home run rates are noisy: a few extra wall-scrapers in a small sample swing the number. xFIP goes one step further and replaces actual home runs with expected home runs, computed from the pitcher's fly-ball rate times the league-average home-run-per-fly-ball percentage. The logic: pitchers control how many fly balls they allow far more than how many of those flies clear the fence.

xFIP is most useful for young pitchers and small samples, where a fluky home run total distorts FIP badly. Over full seasons the two usually converge, because luck evens out. When they disagree sharply, believe xFIP for the underlying skill and FIP for what actually happened. Both beat raw ERA for evaluation, and the gap between all three tells the richest story.

Common FIP Mistakes

First: the wrong constant. The FIP constant changes every season with the run environment; using 3.10 for a season where it was 3.25 shifts every pitcher's FIP by 0.15. Match the constant to the season. Second: small samples. FIP needs innings to stabilize; a 2.50 FIP over 20 innings is mostly noise wearing a precise number.

Third: treating FIP as a complete evaluation. It deliberately ignores balls in play, which means it ignores pitchers who genuinely induce weak contact. Some pitchers beat their FIP for years; the stat's philosophy says that is luck, and sometimes the philosophy is wrong. Fourth: cross-era comparisons without adjusting the constant. Fifth: forgetting the philosophical bet. FIP assumes strikeouts, walks, and homers are the controllable skills. That assumption is well supported, but it is still an assumption, and the best analysts hold it lightly.

A Second Worked Example: The Dominant Reliever

Take a shutdown reliever: 65 innings, 8 home runs, 20 walks, 5 hit batters, 80 strikeouts. The numerator: 13 times 8 is 104, plus 3 times 25 (walks plus HBPs) is 75, minus 2 times 80 is 160. That gives 104 plus 75 minus 160, which is 19. Divide by 65 innings: 0.292. Add the constant 3.10 and the FIP is 3.39, a very good number for a setup man.

Now isolate the home runs to feel the weights. If two of those homers had been doubles instead, the numerator drops by 26 (2 times 13) while everything else stays: negative 7 divided by 65 is negative 0.108, plus 3.10, giving 2.99. Two pitches over the fence cost 0.40 of FIP, which is why relievers who "just give up the occasional homer" grade worse than their ERA suggests. The long ball dominates the formula the way it dominates the game.

Why 13, 3, and 2: The Run Values Behind the Weights

The weights are not round numbers by accident; they come from linear-weights run values measured across millions of plate appearances. A home run is worth about 1.4 runs above an out, a walk about 0.3, and the strikeout-versus-ball-in-play gap about 0.3 in the other direction. Multiply through to put everything on the same scale and you get roughly 13, 3, and 2. The formula is empirical, not aesthetic.

This is also why the weights occasionally get revised. As the run environment changes, the true run values drift: in a low-scoring era, each home run is relatively more damaging. The constant absorbs most of the drift, which is why it hovers near 3.10 but moves yearly. When comparing FIP across seasons, use the season-appropriate constant; a 3.50 FIP in a 3.10-constant year is not the same achievement as 3.50 in a 3.40 year.

FIP vs xFIP vs SIERA: The Alphabet Soup, Sorted

xFIP normalizes the home run rate: it replaces actual home runs with an expected number based on fly balls times a league-average HR/FB rate, typically around 10 to 12 percent. A pitcher with a 3.20 FIP but a 4.00 xFIP has been lucky on fly balls leaving the yard; expect regression. Use xFIP for predicting next season, FIP for describing this one.

SIERA goes further, adding balls-in-play data back in with interaction terms: strikeout rate matters more for high-walk pitchers, for example. It predicts ERA slightly better than FIP in most studies, at the cost of a formula nobody computes by hand. The practical stack: FIP for what happened, xFIP for what should have happened, SIERA for what happens next. The calculator gives you the foundation; the alphabet is the second floor.

When FIP Lies: Small Samples and Contact Artists

FIP needs innings to stabilize, roughly 70 to 100 before the home run rate means much. A reliever with 20 innings and 1 home run has a glittering HR/9 that says nothing; one bad outing rewrites it. Never quote a reliever's FIP before Memorial Day, and treat September call-up numbers as souvenirs, not statistics.

Extreme contact pitchers break the philosophy, not just the sample. A knuckleballer or sinkerballer who lives on weak contact can run ERAs a full run below their FIP for years, because the formula assumes balls in play are luck and for them, the weak contact is the skill. FIP is a great default and a bad religion. When a pitcher beats his FIP for three straight seasons, believe the pitcher, not the formula.