St. Louis Cardinals · P · Pre-arbitration
Riley O'Brien has an estimated 2 years and 121 days of major league service time — 2.121 in the notation clubs use, from 465 days credited on a major league roster.
| Season | Club | Days | Running total | How this season is known |
|---|---|---|---|---|
| 2021 | Cincinnati Reds | 2 | 0.002 | From transactions |
| 2022 | Seattle Mariners | 3 | 0.005 | From transactions |
| 2023 | Seattle Mariners, St. Louis Cardinals | 0 | 0.005 | From transactions |
| 2024 | St. Louis Cardinals | 168 | 1.001 | From transactions |
| 2025 | St. Louis Cardinals | 120 | 1.121 | From transactions |
| 2026 | St. Louis Cardinals | 172 | 2.121 | From transactions |
172 days credit a full year, so a season adds at most 1.000 no matter how long a player is on a roster. 3.000 years reaches salary arbitration and 6.000 reaches free agency —
what every threshold unlocks.
This figure is an estimate reconstructed from public roster
transaction records. It is not an official MLB or MLBPA figure — those are
not published. See the
methodology.
Last updated 2026-10-12.
Independent project, not affiliated with or endorsed by Major League
Baseball or the MLBPA.