What are Pythagorean wins?
The original Bill James formula — the one that named the concept after the Pythagorean theorem because of its PF²/(PF²+PA²) shape. Baseball's best-fit exponent is 1.83, and run differential is the most reliable predictor of future winning percentage in the sport.
How the calculator works
Enter runs scored and allowed over any span; add actual wins to see the luck gap. Teams winning 95 games on a +40 run differential are 2021-mariners-style mirages until proven otherwise.
Common use cases
- Identifying September regression and surprise contenders
- Fantasy: sell closers on lucky teams before the wins dry up
- Offseason win-total arguments with receipts
Formula & caveats
Blowout skew and bullpen leverage patterns create real exceptions, but the mean-reversion pull of run differential is one of baseball's strongest forces.
Frequently Asked Questions
Why 1.83?
It is the exponent that best fits historical MLB records to run differential.
What is 'luck' here?
Actual wins minus expected wins — mostly one-run game records and blowout distribution.
Does it work for a single series?
No — it needs a meaningful sample (40+ games) to say anything.
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