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

Every October, some version of the same take can be heard in all playoff discussions: the team stumbling into the playoffs is doomed, and the team on a roll is a lock to advance. It sounds right. We believe that momentum is a real thing in sports. It makes sense to us that a team playing confidently in September should carry that into the postseason, and a team scuffling through the stretch run would carry that baggage along with it.

So I decided to actually check.

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.

The answer is…

There is essentially no correlation.

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.

The World Series Says the Same Thing

One way to determine who “did well” in the playoffs is to see who advanced the farthest. If momentum truly mattered, then we’d expect the two teams that made it to the World Series to be teams that were playing well to end the year. Instead, the nine World Series matchups show no real connection to September success. Some World Series participants had September OPSs as high as .882 (2019 Astros), and some were as low as .696 (2024 Yankees). In fact, six of the 18 participants had truly poor September OPS marks under .740. The 2022 Astros still won the whole thing.

The best example of how September performance doesn’t correlate is the 2023 Diamondbacks. They reached the World Series despite having the single worst September OPS of any of the 12 playoff teams that year. Back in 2017, the Dodgers had the 9th-best OPS of the 10 playoff teams in September, with an 11th-percentile finish to the regular season, and still won the NL pennant. The 2021 Braves won the whole thing with the worst September OPS of any NL team at .766; that was a 22nd percentile OPS in all of baseball that month.

If we look at the inverse and assume early exits were limited to poor September teams, we would also be wrong. Of the nine champions in this little study, only four actually rode really above-average Septembers to a title: the 2019 Nationals, the 2023 Rangers, and the 2024 and 2025 Dodgers. There just doesn’t appear to be any throughline here.

The Cold Teams That Got Hot at the Right Time

If we were to expand beyond just the teams that made the World Series, we see more examples of how a bad September wasn’t actually a red flag.

The 2025 Tigers are the extreme case. They finished September with a record of 7-17. That’s a .292 winning percentage that is, by far, the worst September of any playoff team in nine years I looked at. Yet, they still won their Wild Card series and advanced to the Division Series. The 2024 Royals weren’t much better by OPS, posting a .577 mark that’s the lowest of any playoff team in this entire sample, and they also won their first playoff series.

The 2022 Phillies might be a useful comparison for a few teams in the 2026 postseason, like, say, the 2026 Phillies. The 2022 team limped into October with a 11-14 record in September. They have a below-average but not brutal OPS yet still had one of the worst records in that year’s playoff field. Yet, they just kept winning and made the World Series. Could we see something similar for the 2026 Phillies, Cubs, or Red Sox? Three teams that had been pretty strong for most of the season (OK, late June on for Boston) but struggled with poor finishes to the season?

The Hot Teams Have Also Gone Home Early

The other half of the argument is perhaps more surprising, because it’s the situation that the “backing in” theory says shouldn’t happen. Many teams that were rolling right into the playoffs still lost their very first series.

The 2021 Cardinals are the best example. They finished the regular season with a 22-7 month of September. Their .759 winning percentage is the third-best in the entire nine-year dataset. They also backed that up with a strong .799 team OPS, which was 67th percentile among that year’s playoff field. All of that earned them one game: a 3-1 loss to the Dodgers in the single-elimination Wild Card round. (Yes, perhaps that’s an example of why the three-game series makes some sense).

The 2022 Blue Jays team makes the same point, mostly. Yes, Toronto’s 18-10 record wasn’t as impressive as St. Louis’, but it wsa a strong mark, and the Blue Jays also had a .804 team OPS in September, which was the single best mark of any playoff team that year. Still, the Blue Jays were swept out of the Wild Card round in two games, losing to the Mariners 4-0 and 10-9.

A few more examples listed above: the 2017 Twins (.805 OPS, 78th percentile) and the 2018 A’s (.800 OPS, also 78th percentile) both turned strong Septembers into first-round exits. The Twins lost 8-4 to the Yankees, while the A’s actually did this in back-to-back years. The 2018 A’s were 97-65 and had a great September, but lost 7-2 to the Yankees in the Wild Card round, and the 2019 A’s were also 97-65 (yes, for real), and took an even stronger September into a 5-1 loss to the Rays.

So What Does September Actually Tell Us?

Not much, at least not about October. The best explanation isn’t that momentum doesn’t exist. Teams clearly can and do get hot or cold in ways that we can see with our own eyes. Just think about the New York Knicks’ NBA title run a few months ago. However, what we can say is that a 25-or-30-game sample in September doesn’t predict a short playoff series decided by small details like what starting pitcher is lined up, which bullpen is more effective, which manager makes the better pinch-hit decision, and myriad other small decisions that impact a baseball game.

And what does this mean for the 2026 postseason?

Well, obviously, nothing. Any of these teams could go on a run, but it’s smarter to favor season-long success over September success. That means teams like the Cubs, who had the best wRC+ in baseball this season, or the Dodgers, who were second in both wRC+ and OPS, stand a better chance of making a deep run than the Padres, who had the best record in September and were second in wRC+, or the Guardians, who finished with a .640 winning percentage in September, the fifth-best in the league.

Of course, teams like the Dodgers and Brewers have been atop the leaderboards in September and also in season-long leagues, which is often the best indicator of a team that is truly built to make a deep playoff run.