Key takeaways
- Read FIP as an estimate of the ERA a pitcher would have posted with league-average defence, luck on balls in play and sequencing behind him.
- Treat a large gap between ERA and FIP as a question to investigate, not as proof of luck: some pitchers have real skills that FIP leaves out.
- Compare a FIP only with the same season's league ERA, or use a park- and league-adjusted version such as FIP-, because the raw number moves with the run environment.
- Reach for xFIP when you suspect home-run luck, and remember that a minority of pitchers genuinely control how many of their fly balls leave the park.
- Quote ERA when the question is what happened, and FIP when the question is how well the pitcher pitched.
ERA tells you how many earned runs scored while a pitcher was on the mound; FIP estimates what his ERA would have been if his defence, his luck on balls in play and the order of events had all been league average. FIP — fielding independent pitching — does that by throwing away every ball hit into the field of play and keeping only four outcomes: strikeouts, walks, hit batters and home runs.
So the honest answer to "FIP vs ERA" is that they answer different questions. ERA is the record. FIP is an estimate of the pitcher's share of that record. Over a long career the two usually end up close together, as FanGraphs' library notes, but over a single season they can sit a long way apart, and the gap is where the useful information lives.
What ERA folds in alongside the pitcher
MLB's glossary defines ERA as nine times earned runs divided by innings pitched, where an earned run is one that scored without the aid of an error or a passed ball. What is ERA in baseball covers the calculation and the earned/unearned boundary in detail. The point here is what else ends up inside the number.
The fielders. The earned-run rule removes runs caused by errors, but, as MLB's own glossary puts it, defensive mistakes are accounted for while "great defensive plays are not." A shortstop with limited range commits no error on the ball he never reaches, so the pitcher wears the hit in full.
Luck on balls in play. A softly hit ball can find a gap; a hard line drive can find a glove. The pitcher's influence ends once the ball leaves the bat far more than most fans assume, which is the research finding FIP rests on.
Sequencing. Runs depend on the order of events, not just the events. With two out and the bases empty, a walk, a walk and a home run produce three runs. A home run, a walk and a walk produce one. The pitcher threw identical outcomes in both innings, and his ERA moved by different amounts.
FIP's premise, set out in FanGraphs' FIP entry, traces back to research by Voros McCracken in the early 2000s: the rate at which balls in play fall for hits against a pitcher does not correlate well from one season to the next. If that rate is mostly not his doing, a statistic that leaves it out describes the pitcher more cleanly.
How FIP is calculated
FanGraphs and MLB.com publish the same formula:
FIP = ((13 × HR) + (3 × (BB + HBP)) − (2 × K)) ÷ IP + constant
The weights are not arbitrary. FanGraphs says they reflect the relative run-prevention value of each event: a home run is far more damaging than a walk, and a strikeout is an out that never gives the defence, or luck, a chance to intervene.
The constant
The raw weighted total is not on a familiar scale, so a constant is added to make FIP read like ERA. FanGraphs describes it as "solely to bring FIP onto an ERA scale" and says it is "generally around 3.10". It is recalculated every season so that league-average FIP equals league-average ERA:
FIP constant = lgERA − ((13 × lgHR) + (3 × (lgBB + lgHBP)) − (2 × lgK)) ÷ lgIP
That design choice matters when you compare seasons, and it is the reason a "good" FIP has no fixed value.
A worked example
Take a hypothetical starter with 180 innings, 190 strikeouts, 50 walks, 6 hit batters and 20 home runs allowed, and use 3.10 as an illustrative constant (the real one depends on the season).
| Step | Arithmetic | Result |
|---|---|---|
| Home-run term | 13 × 20 | 260 |
| Walk and hit-batter term | 3 × (50 + 6) | 168 |
| Strikeout term | 2 × 190 | 380 |
| Weighted total | 260 + 168 − 380 | 48 |
| Per inning | 48 ÷ 180 | 0.27 |
| FIP | 0.27 + 3.10 | about 3.37 |
Suppose the same pitcher's ERA was 4.10. A gap of roughly three quarters of a run says the runs he allowed were not driven by his strikeouts, walks or home runs. Something on balls in play, or in the order of events, cost him. To run the same arithmetic on a real line, the pitching stats calculator computes FIP once you supply the season's constant, or works the constant out from league totals.
Reading the gap between ERA and FIP
| What each statistic does with… | ERA | FIP |
|---|---|---|
| A strikeout | An out like any other | Lowers it (weight −2) |
| A walk or hit batter | Hurts only if the runner scores | Raises it (weight 3) |
| A home run | Counts every run it drives in | Raises it heavily (weight 13) |
| A single on a ball in play | Hurts only if it leads to a run | Ignored |
| A great defensive play | Helps, invisibly | Ignored |
| An error | Its runs are excluded as unearned | Ignored |
| The order of events | Fully reflected | Ignored |
ERA well above FIP usually points to hits on balls in play, weak defence or bad sequencing. MLB's glossary gives the plainest version: a pitcher who has allowed a high average on balls in play will likely have a FIP lower than his ERA.
ERA well below FIP is the case to treat with more care. Some of it is good defence and good fortune. But FanGraphs is explicit that some pitchers beat their FIP for real reasons — holding the running game, or generating fly balls at the expense of line drives and ground balls. FIP cannot see those skills.
A short sample weakens both. FanGraphs notes FIP is more appropriate over a season's worth of innings than over a single game, and MLB's ERA entry warns that ERA is less effective for relievers, who often pitch only fractions of an inning and leave runners for someone else to strand or allow home.
A three-question check before you trust either number:
- How many innings is this? Fewer than a season's worth and both figures are noisy.
- Is the gap explained by balls in play? If the batting average on balls in play against him is far from normal, the gap is probably not repeatable.
- Does this pitcher have a known FIP-beating trait? Fly-ball tendencies and control of the running game are the documented ones.
xFIP: taking the home runs out of the luck too
FanGraphs credits xFIP to Dave Studeman of The Hardball Times. It keeps FIP's structure but swaps a pitcher's actual home runs for an estimate: his fly balls multiplied by the league-average home-run-per-fly-ball rate, which FanGraphs puts between 9 and 10 percent depending on the year.
xFIP = ((13 × (FB × lgHR/FB)) + (3 × (BB + HBP)) − (2 × K)) ÷ IP + constant
Continue the example. If our hypothetical starter allowed 180 fly balls and the league rate were 10 percent, he would be expected to allow 18 home runs rather than the 20 he did. His xFIP would be (234 + 168 − 380) ÷ 180 + 3.10, or about 3.22 — a little better than his FIP, because two of his home runs are treated as bad luck.
The distinction FanGraphs draws is useful: FIP describes how a pitcher performed independent of his defence, while xFIP is closer to an estimate of how well he pitched. The catch is that a minority of pitchers really do allow fewer, or more, home runs per fly ball year after year, and xFIP will misjudge them. Its data also only reaches back to 2002, when reliable fly-ball tracking begins.
What counts as a good FIP
Because FIP is designed to match league ERA, "good" is relative to the season. FanGraphs publishes a rough guide calibrated to the 2016 run environment, which puts an average FIP at 4.20, an excellent one at 3.20 and an awful one at 5.00. In a lower-scoring season every one of those thresholds drops. FanGraphs also points out that FIP is not adjusted for park or league, so a pitcher in a pitcher-friendly park will look better than he is. Its answer is FIP-, which re-scales FIP so 100 is league average after a park adjustment, and — because lower is better for pitchers — every point below 100 is a percentage point better than average.
When ERA is still the right number
FIP is not a correction to ERA so much as a different measurement, and there are questions only ERA answers.
What actually happened. If you want to know how many runs scored while a pitcher was on the mound, ERA is the record, and FanGraphs itself says ERA does a terrific job of telling you exactly that.
Valuing a season, depending on whose method you use. This is where publishers genuinely differ. MLB's WAR glossary notes that FanGraphs' WAR uses FIP for pitchers while Baseball-Reference's uses runs allowed per nine innings. FanGraphs' own WAR calculation goes a step further and counts infield fly balls as strikeouts inside its FIP, and it also publishes an RA9-based WAR for readers who prefer runs allowed. Neither choice is wrong; they reflect different views on how much credit a pitcher deserves for balls in play.
Pitchers FIP does not describe well. If a pitcher has years of evidence that he beats his FIP, the evidence beats the formula.
What is WHIP in baseball covers the third common pitching rate. It counts baserunners rather than runs, so it removes sequencing, but unlike FIP it still includes every hit on a ball in play.
Using the idea without the number
162-0 Baseball Draft & GM Team has you compare pitchers on ERA, WHIP and WAR, among other numbers, so FIP thinking there is a question to ask of those figures: how much of this ERA might the defence have produced? Defence is one of the inputs the game's season simulator weighs, alongside pitching, hitting, speed, position fit, roster quality and coaching, so the projection counts the fielders you draft as well as the arms. The baseball draft simulator guide works through reading ERA and WHIP together on a draft card.
If you are the pitcher rather than the general manager, the season record in Baseball Career Sim 2026 tracks ERA, WHIP and strikeouts across your career. Strikeouts are the part of that line most purely your own, which is the whole insight behind FIP. Baseball stats explained for beginners covers the rest of the standard vocabulary, and more on the sport is collected on our baseball page.
Baseball Career Sim 2026 is set in a fictional league with fictional teams and players. 162-0 Baseball Draft & GM Team builds its player pool from real players' careers, with ratings that are the game's own estimates. Neither game is affiliated with or endorsed by any league, team, players' association or player. MLB.com and FanGraphs are named only to identify the definitions cited here. Our other management and career titles are in sports career and GM games.
Good to know
Frequently asked questions
What is the difference between FIP and ERA?
How do you calculate FIP?
What is a good FIP in baseball?
Is FIP better than ERA?
What is xFIP?
Sources
- FIP | Sabermetrics Library (opens in a new tab)FanGraphs — accessed
- xFIP | Sabermetrics Library (opens in a new tab)FanGraphs — accessed
- Fielding Independent Pitching (FIP) | Glossary (opens in a new tab)MLB.com — accessed
- Earned Run Average (ERA) | Glossary (opens in a new tab)MLB.com — accessed
- ERA- / FIP- / xFIP- | Sabermetrics Library (opens in a new tab)FanGraphs — accessed
- WAR for Pitchers | Sabermetrics Library (opens in a new tab)FanGraphs — accessed
- Wins Above Replacement (WAR) | Glossary (opens in a new tab)MLB.com — accessed
League, team and athlete names appear here only to identify the rules, records and history being discussed. Reign Creative LLC's sports games are not affiliated with, endorsed by or licensed by any league, team, players' association or athlete, and all names and marks belong to their owners.
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