MLB Postseason 2026: Does regular-season momentum matter in the playoffs?

I pulled every MLB playoff team from the last nine full seasons (2016 through 2025, skipping the COVID-shortened 2020 season). That gave me 98 "seasons" using two different playoff formats. For each team and year, I pulled stats to show "how good was their September." For that, I decided to use both winning percentage and their team OPS that month. Then also pulled stats to show "how did they fare in the postseason?" For that, I used the round they were eliminated in, as well as their overall postseason winning percentage. After doing that, I cross-referenced the numbers to see if there was any connection.

These correlations are represented through a Pearson correlation, which I just learned about this week. It's basically a measure of how closely two things move together. In this case, 1.0 would mean September winning percentage and playoff success are perfectly linked, and 0 would mean they have nothing to do with each other. When I compared September winning percentage to playoff advancement, I got a score of 0.020, which is essentially zero. There was no connection.

I then checked September winning percentage against postseason winning percentage and got 0.004. Even less of a connection than to playoff advancement. I then checked September team OPS to playoff round reached and got 0.186, which was a little better, but still not great. Lastly, I checked September OPS against playoff winning percentage and got 0.052. All of which is to say, however you slice it, a team's September tells you almost nothing about what its October will look like.