How to count days on option?

 A player's days on minor league option are counted as total of each season, and the number of days only meaningful whether it is 20 or more. If 20 or more than 20, his "option" is used, while if less than 20, his "option" is not used and his option days are added to his major league service time.

However, if a player's number of days on option is close to 19-20 borderline, it may be difficult to judge whether his "option" is used or not used.  

The counting method is described in ARTICLE XIX-E and ATTACHMENT 32 of collective bargaining agreement.

 To summarize, there are 8 conditions below to count a player's days on option

1. The date of optional assignment is counted as day-1.
2. If a player is optioned during spring training, his days on option are not counted until the opening day.
3. If a player has been optioned at the time of his club's opening day,  the date of that season's earliest opening day is counted as day-1.
4. If a player is optioned after the game, that date is NOT counted (day-zero).
5. The date of recall (or recall, not to report) is NOT counted.
6. If a player is recalled, not to report and designated for assignment, the date is counted (as the last day).
7. If a player is recalled, not to report and released, the date is counted (as the last day).
8. If a player is recalled, not to report and outrighted, the date is NOT counted.

Specific examples of counting days on option

Case 1: Jedd Gyorko

In 2015, San Diego Padres optioned him on June 10, and recalled on June 30 (Source).

June 10 was counted, and June 30 was not counted (per condition 1&5). His days on option were from June 10 to June 29, just 20 days.

So he was used one "option" in 2015.

 

Case 2: Lance McCullers Jr.

In 2015, Houston Astros purchased him on May 18, then optioned on August 3, and recalled on August 23 (Source)

. However, his optional assignment took place after the game of the day, so that transaction was effective the next day.

August 3 was not counted (per condition 4), and August 23 was not counted (per condition 5). His days on option were from August 4 to August 22, just 19 days.

So he was not used any "option" in 2015.

 

Case 3: Grant Dayton

In 2015, Miami Marlins optioned him on March 13,  and he failed to make Marlins' opening day roster. Marlins then recalled him (not to report) and designated for assignment on April 24, and outright on April 26 (Source). The earliest opening day in 2015 was April 5.

April 5 was counted as day-1 (per condition 2&3), and April 24 was also counted (per condition 6). His days on option were from April 5 to April 24, just 20 days.

So he was used one "option" in 2015.