Do late-season hot streaks matter in playoffs?

By the time the MLB postseason starts on Oct. 3, the dust will have settled on an action-packed regular season, as well as the ebbs and flows that come with it. Winning and losing streaks alike will be things of the past.

But some of those especially hot or cold teams will play on. The question is whether success down the stretch translates into postseason glory. More broadly, does late-season “momentum” -- or a lack thereof -- carry over into the playoffs? Let’s look back at recent history and see what it means for this year's postseason field.

Note: Mentions of "September" or the "final month" refer to regular-season games played in both September and October.

How has the hottest team fared?
In the 10 previous full seasons since the second Wild Card was introduced (2012-22), only the '12 Giants and '22 Astros went on to win it all after posting the best final-month winning percentage among playoff teams. Of the other seven “hottest” teams, only the '19 Astros even made it to the World Series.

Hottest playoff teams by final-month record (in the multi-Wild Card Era, since 2012)
2022 Astros (22-9) -- won World Series
2021 Giants (23-7) -- lost NLDS
2020 Dodgers (17-7) -- won World Series
2019 Astros (19-6) -- lost World Series
2018 Astros (21-6) -- lost ALCS
2017 Indians (26-4) -- lost ALDS
2016 Red Sox (19-10) -- lost ALDS
2015 Cubs (23-9) -- lost NLCS
2014 Nationals (19-8) -- lost NLDS
2013 Indians (21-6) -- lost ALWC
2012 Giants/Braves (20-10) -- won World Series/lost NLWC

So while it certainly doesn't hurt to hit your stride during the stretch run -- just ask last year's Astros -- it hardly guarantees a title is in a team's future.

What about the coldest team?
Final-month records can admittedly be deceiving, as teams that clinch a postseason berth early might rest players once their playoff seeding is settled. For example, the 2015 Royals were the first team to clinch a division title when they locked up the AL Central on Sept. 24, and they still retained home-field advantage throughout their championship run despite posting a 15-17 record to close the regular season. They are the only team in the multi-Wild Card era to win a World Series after going under .500 in the final month.

Coldest playoff teams by final-month record (in the multi-Wild Card Era, since 2012)
2022 Rays (14-19) -- lost ALWC
2021 Brewers (14-15) -- lost NLDS
2020 Astros (10-17) -- lost ALCS
2019 Yankees / Braves (14-11) -- lost ALCS / lost NLDS
2018 Indians (14-14) -- lost NLDS
2017 Twins / Rockies (15-14) -- lost ALWC / lost NLWC
2016 Blue Jays (13-16) -- lost ALCS
2015 Astros (13-17) -- lost ALDS
2014 A's (10-16) -- lost ALWC
2013 Dodgers (12-15) -- lost NLCS
2012 Rangers (15-16) -- lost ALWC

On the other hand, four of the 10 World Series winners during that span actually ranked among the bottom half of all playoff teams in final-month winning percentage. The only team to win the World Series from the second Wild Card slot was the 2014 Giants, and they backed into playoff position by dropping the NL West lead on July 26 and going 30-28 afterward, including 13-12 in September.

Do eventual champions finish strong?
Incredibly. Or not at all. It depends. In terms of winning percentage, teams such as the 2012 Giants and '17 Astros were at least 85 points better across the season’s final month than they were overall. At the same time, teams such as the '15 Royals and '18 Red Sox were just as far off their full-season record in the other direction, but nonetheless “flipped the switch” and went on to hoist the Commissioner's Trophy once everything was said and done.

Every other team in the second Wild Card Era found itself somewhere in between. Even champions -- such as the 2019 Nationals (who clawed back from a slow start) and the '16 Cubs (who posted a dominant 50-23 second-half record) -- weren’t markedly better in the final month than their overall record, despite feeling like teams that created momentum heading into the playoffs.

At FanGraphs, Jay Jaffe pooled together the numbers all the way back to the 1995 season and found that the results remained the same, adding that “[final-month] winning percentages just don’t tell us very much at all about what happens in [the playoffs].”

What are the implications of Game 162?
Some teams may have a lot on the line on the final day of the regular season. But does the result of that 162nd game matter once the postseason begins? Almost certainly not. And yet, recent seasons have seen a curious trend.

Each of the past nine World Series winners won their final regular-season game. The same goes for 18 of the past 20 AL or NL pennant winners, with the lone exceptions being the 2012 Giants and the '13 Red Sox.

In conclusion
Momentum may be a myth, but the confidence that comes with being a successful team winning big games late in a season is still very real. Per FanGraphs, the average win percentage of a pennant-winning team between 1995 and 2019 was .590 from the start of a season through August and .591 over the final month. So while a team hustling to the finish line or coasting in may not be predictive of postseason success, the overall records of the past 50 pennant winners average out to that of about a 96-win team. Simply put, the cream rises to the top.