● EXPLAINER · BY MARCDUCK

What is ERA+ in MLB Betting?

Published June 2, 2026 · Updated October 3, 2026

ERA+ is ERA adjusted for park factor and league average, scaled so 100 equals league average and 150 means 50% better than league. ERA+ makes pitcher ERA comparable across parks and seasons.

What ERA+ Measures

Raw ERA varies hugely by park and era. A 3.50 ERA at Coors Field is much more impressive than a 3.50 ERA at Petco Park, where league-average pitchers post sub-4.00 ERAs by default. ERA+ corrects for that by dividing the league-average ERA by the pitcher's ERA and adjusting for the pitcher's home park.

The formula: ERA+ = 100 × (lgERA × park_factor) / pitcher_ERA. The 100 anchor means league average is always 100; higher is better. (Note the inversion vs OPS+ where higher hitter values are higher numbers; ERA+ also goes up as the pitcher gets better, even though raw ERA goes down.)

How to Read ERA+

180+: historic season (Cy Young tier, rare)
150-180: All-Star ace tier
120-150: above average starter
100-120: league average
80-100: below average / back-end starter
Below 80: poor / fringe rotation

Why ERA+ Matters for Betting

ERA+ is comparable across pitchers from different parks. A 3.20 ERA pitcher in Coors has roughly the same ERA+ as a 2.80 ERA pitcher in a pitcher-friendly park. Without ERA+, the betting market overrates pitchers in pitcher parks and underrates those in hitter parks.

For ranking starters across the league or comparing rotation depth between two teams, ERA+ gives true apples-to-apples.

ERA+ vs FIP and xERA

ERA+: park- and league-adjusted ERA. Captures everything that happened, including defense and BABIP luck.
FIP / fipMinus: strips defense and BABIP luck out. More predictive of future performance.
xERA: uses Statcast quality-of-contact data. Most sophisticated single ERA estimator.

ERA+ describes the past well. FIP and xERA predict the future better. Sharp models use FIP/xERA as primary inputs and ERA+ as a secondary descriptive check.

The Park Adjustment

Park factor scales ERA+ both ways. A pitcher in Petco (a park factor below 1.00) has a smaller park-adjusted league average divided by his ERA: making his raw 3.00 ERA look LESS impressive in ERA+ terms because the league ERA there is naturally lower. The opposite for Coors. ERA+ removes the park-dependent illusion.

How Bookie Bullies Uses ERA+

ERA+ is not an input in the current model. For starting pitchers the model uses an effective run rate built from FIP, xFIP and Statcast xERA, with the starter gap weighted 85% on that rate and 15% on raw ERA, plus times-through-the-order, K-BB%, BABIP and LOB% terms and lineup-vs-handedness splits.

Apply This Today

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