ERA Predictor
See how your next outing changes your ERA
Start with your season line, add a projected or completed outing, and compare your current ERA with the new one.
Projected ERA
Current ERA
36 ER · 90 IP
New ERA
37 ER · 97 IP
Current ERA 3.60. Projected ERA 3.43. 0.17 lower.
Current vs projected
- Current
- 3.60
- Projected
- 3.43
Season totals after the outing: 37 ER over 97 innings (291 outs).
How it works
Add outs, add runs, recalculate
Your new ERA isn't an average of two ERAs. It comes from the combined totals: (current ER + outing ER) × 27 ÷ (current outs + outing outs). Working in outs keeps partial innings exact — 5.2 innings plus 1.1 innings is 21 outs, or 7.0 innings.
For example, a pitcher with 36 earned runs in 90 innings has a 3.60 ERA. After a 7-inning, 1-run start, the totals are 37 earned runs in 97 innings, for a new ERA of 3.43.
The same outing moves ERA more early in a season, when it's a bigger share of total innings, and barely at all late in a long season.
FAQ
ERA predictor questions
How do I calculate my new ERA after a start?
Add the outing's earned runs to your current earned runs and the outing's outs to your current outs, then apply ERA = earned runs × 27 ÷ outs. The predictor does this automatically and shows the change.
Why does one bad outing move ERA so much early in the season?
ERA is an average, so each new outing is weighted by how many innings it adds relative to what you've already thrown. With 10 innings pitched, a 5-inning outing is a third of your total; with 150 innings, it barely registers.
Can I use my season totals from a stat site?
Yes. Enter earned runs and innings pitched exactly as listed, including .1 and .2 notation. If you only know your ERA and innings, earned runs = ERA × innings ÷ 9, rounded to the nearest whole number.