What is ERA+? Definition, Formula, and Example
ERA+ (Adjusted ERA Plus) is a park- and league-adjusted version of ERA where 100 equals league average and every point above 100 means the pitcher allowed 1% fewer runs than a typical pitcher in the same conditions.
What is ERA+?
ERA+ (Earned Run Average Plus) is a pitching statistic that normalizes a pitcher's ERA against the league average and adjusts for the run-scoring environment of their home ballpark. A value of 100 is exactly league average. A pitcher with an ERA+ of 150 allowed 50% fewer runs than an average pitcher would have in the same parks and league context. The higher the ERA+, the better.
How ERA+ Is Calculated
Baseball Reference defines ERA+ as:
ERA+ = 100 × (lgERA / ERA)
where lgERA is the park-adjusted league ERA — the ERA a league-average pitcher would have recorded if they had the same home/road split as the pitcher being evaluated.
In practice the formula is:
ERA+ = 100 × [(lgERA ÷ park factor) ÷ ERA]
Park factor is a multiplier derived from the ratio of runs scored in a pitcher's home park vs. the rest of the league. A park factor above 1.0 inflates ERA; below 1.0 deflates it. ERA+ corrects for this, so pitching in Coors Field and pitching in Petco Park get fair treatment.
Worked Example: Jacob deGrom 2021
Jacob deGrom's 2021 season is one of the most extreme ERA+ seasons on record. He posted a 1.08 ERA in 15 starts before injury ended his year. The NL ERA that season was approximately 4.10. Applying park adjustments for Citi Field (a mild pitcher's park), deGrom's ERA+ landed at 287 — meaning he was 187% better than the league-average pitcher. Only Pedro Martínez's 2000 season (1.74 ERA, ERA+ of 291) rivals it in the modern era.
A league-average starter lands between 95 and 105 ERA+ in most seasons. An ERA+ above 130 is All-Star caliber. Above 160 is Cy Young territory. Career ERA+ above 130 is a Hall of Fame argument.
Why ERA+ Matters
ERA+ solves two problems ERA cannot: era comparison and park distortion. Bob Gibson's 1.12 ERA in 1968 came in the Year of the Pitcher when scoring was historically suppressed — his ERA+ of 258 reflects dominance relative to peers, not just a low absolute ERA. Conversely, a pitcher who posts a 3.80 ERA at Coors Field may have an ERA+ of 120, reflecting genuine quality the raw number hides.
Front offices use ERA+ to compare pitchers across decades for contract valuation and Hall of Fame candidacy. Fantasy analysts use it to quickly gauge whether a pitcher's ERA is sustainable or artificially inflated by park or era effects.
In Legends Deck: ERA+ feeds directly into the pitching effectiveness rating on pitcher cards. A career ERA+ of 155+ unlocks the top "Ace" tier. Cards from a pitcher's best individual seasons display that season's ERA+, allowing collectors to identify peak-value cards from historically dominant campaigns.
Limitations and Misconceptions
ERA+ is still grounded in ERA, which is partly a function of fielding quality. A pitcher with poor defense behind him can have a depressed ERA+ through no fault of his own. ERA+ also doesn't isolate contact luck — a pitcher who surrendered a lot of hard contact but stranded runners will show a better ERA+ than his true skill warrants.
ERA+ should not be confused with FIP or xFIP, which strip out fielding and use only strikeouts, walks, and home runs. ERA+ adjusts context; FIP removes defense. They answer different questions.
Finally, ERA+ is a Baseball Reference metric. FanGraphs uses ERA- (lower is better, same concept) for the same purpose — a common source of confusion when switching between platforms.