What is a September Call-Up? Definition and Examples
A September call-up is a minor league player added to the MLB active roster when rosters expand on September 1 — from 26 to 28 players under current rules — letting teams audition prospects and add depth for the playoff push.
What is a September Call-Up?
A September call-up is a player promoted from the minors to the major league roster when MLB active rosters expand on September 1. Under the current collective bargaining agreement (since 2020), rosters grow from 26 to 28 players, with a maximum of 14 pitchers. Before 2020, teams could carry anyone on their 40-man roster — sometimes 35+ players — which is why "September call-ups" historically meant waves of prospects flooding big-league dugouts for the season's final month.
How September Call-Ups Work
The mechanics:
1. On September 1, every club's active roster expands from 26 to 28.
2. Players called up must already be on the 40-man roster; adding a prospect who isn't requires a corresponding 40-man move (a DFA, 60-day IL transfer, or outright assignment).
3. Called-up players accrue MLB service time for every day on the active roster — a major strategic consideration, since a September of service can push a player closer to arbitration and free agency, and can affect Super Two status.
4. Postseason eligibility: players on the 40-man roster (or 60-day IL) as of August 31 are generally eligible for playoff rosters.
Worked Example
The most famous September call-up ever: Fernando Tatis Jr. wasn't one — but his father hit two grand slams in one inning as a September story. A better modern case: in 2019, the Astros called up top prospect Yordan Alvarez — actually June — so take instead 2022's Michael Harris II, no… The cleanest true example: Jacob deGrom debuted in May. The canonical one is Buster Posey, who got a September 2009 cup of coffee (7 games) before winning Rookie of the Year in 2010 — a textbook "get his feet wet" call-up. More recently, contenders use the two extra spots surgically: a third catcher, a pinch-running specialist (Terrance Gore built a career on September/October speed), or a fresh reliever for a bullpen grinding through 162 games.
Why It Matters
September call-ups are where fans get their first look at farm system talent, and they're a front-office chess match: calling up a top prospect "starts the clock," while leaving him down delays free agency by a year. For fantasy players, September call-ups are waiver-wire gold — a prospect getting everyday at-bats for a eliminated team can swing fantasy playoffs.
Limitations and Misconceptions
The post-2020 two-player limit means the old image of 15 call-ups and 40-pitcher games is dead. Also, a September debut doesn't mean a prospect has "made it" — many September call-ups are organizational depth rewarded with a cup of coffee, not future regulars.
In Legends Deck
Legends Deck's season mode mirrors the real calendar: on September 1 your roster expands to 28, and the sim surfaces your top Double-A and Triple-A cards as call-up candidates — complete with service-time warnings when a promotion would start a prospect's clock.
Related terms: 40-man roster, service time, farm system, arbitration, Super Two