Two. That’s the whole answer. MLB active rosters go from 26 players to 28 on September 1, and the pitcher limit rises from 13 to 14.
The question gets asked because it used to be a very different number.
The Limits
| Before Sept. 1 | From Sept. 1 | |
|---|---|---|
| Active roster | 26 | 28 |
| Maximum pitchers | 13 | 14 |
| Doubleheader roster | 27 | 29 |
| Spots optional? | — | No — all 28 must be filled |
That last line matters. Filling all 28 is mandatory, so no club can gain an edge by carrying fewer players. Under the old system, expansion was optional and teams expanded by wildly different amounts.
The Pitcher Cap Shapes Everything
Because the pitcher limit rises by only one, a club can add at most one arm and must make the second addition a position player. That single constraint decides the shape of nearly every September roster in baseball.
For a contender the standard answer is one extra reliever plus a third catcher — the catcher being what lets a manager pinch-hit late without stranding himself if his starter gets hurt.
The Other Requirement
Whoever comes up must already be on the 40-man roster. A club with a full 40 has to clear a spot first, which is a real cost and frequently the reason a top prospect stays in Triple-A. Our page on whether call-ups must be on the 40-man covers that in detail.
How Many It Used to Be
Until 2020, September rosters expanded to the full 40. A club could activate every player under major league contract, and some did — leading to Septembers where one team dressed 39 players and its rival dressed 31.
That disparity, along with the endless pitching changes it enabled, is why the rule changed. Our explainer on why MLB ended 40-man September rosters covers the reasoning.
The Taxi Squad Wrinkle
One extra provision applies year-round rather than just in September: clubs may carry up to five additional players on road trips as a taxi squad. Those players travel and can be activated if needed but do not count against the 28.
Qualifying two-way players also do not count against the pitcher limit, which is a narrow exception affecting very few players.
The Bottom Line
MLB teams can call up exactly two extra players in September, taking the active roster from 26 to 28, with the pitcher cap rising from 13 to 14. All 28 spots must be filled, and every addition must already be on the 40-man roster.