Imagine you have a player with 300 PA, and you are interested in both maximizing his regular season usage AND having him as rested as possible for the playoffs. I know you can "save" up to 5% of his PA for the playoffs, but is that off of the 300 PA, or the PA + 10% cushion? I've been doing the safe thing, and cutting the guy off at 285 regular-season PA, but maybe I could have used him more, going up to (approximately) 315 regular-season PA, and still have him fully rested for the playoffs? Thanks for any thoughts on this--I didn't see it elsewhere in the forums.

I'm not completely sure, but my understanding is that when the playoffs start, it accelerates the usage of all players to 95% of their real-life PA or IP, unless, of course, they are already over that number. If that is the case, you have been handling it correctly to keep your guy at 100% throughout the season and playoffs.

I believe mattedesa is correct

That's the way it was explained several years ago but it doesn't match my experience. I've had well rested low PA hitters who didn't live up to that formula.

From one of contrarian23's pinned threads

https://www.whatifsports.com/forums/Posts.aspx?TopicID=434633

Posted by rbow923 on 9/26/2018 9:01:00 PM (view original):
That's the way it was explained several years ago but it doesn't match my experience. I've had well rested low PA hitters who didn't live up to that formula.

You can't bank PA. It does seem though that the Sim does give a bit extra for each playoff round you reach, be it pitches or plate appearances.

the fat guys get extra PA.

I have a couple of low-PA guys on a current playoff team, it might be worth calculating their percentages:

1989 Alex Trevino, 141 PA/162, 114 regular season PA (81%), 17 postseason PA in 4 games, 131 total PA in 166 team games = 128 PA/162 = 91% of real-life pace. He is listed as being "on pace for 2% more PA (143) than actual PA/162 total." 2% ahead of real-life would project to 147.4 PA per 166 games. Subtracting his 17 postseason PA, I read that as meaning he was treated as having 130 PA when he entered the playoffs. 130/141=92%. If he is treated as being 169 games into the season (we only needed 4 games in a best-of-seven), being 2% ahead of pace projects to 150 PA / 169 games. Subtracting his 17 postseason PA, that gives 133 PA entering the postseason, 94% of his real-life pace. With potential rounding errors, that could be consistent with the 5% of real-life PA being saved.

1989 Edgar Martinez, 196 PA/162, 199 regular season PA (101%), 16 postseason PA in 4 games, 215 total PA in 166 team games projects to 210 PA/162. He is listed as being "on pace for 5% more PA (206) than actual PA/162 total." If his 215 PA were projected over 169 games (162 + 7-game series), that would work out to 206/162.

So both examples tell me that after a round of the playoffs, fatigue is computed as if the season were 7 games further along for a best-of-seven series, even if the series did not last 7 games. The Trevino example is consistent with him being treated as if he'd used 95% (or 94%, plus potential round off error) of his real-life PA/162 before the postseason started.

Getting back to the original question of how much a player should be rested when entering the playoffs, you should consider how many games (and how many PA) he might accumulate during the playoffs. 3 rounds of playoffs could last 19 games, so you want the player to still be at 100% performance (110% of his PA/162) after 18 postseason games... after 180 total games. Generously assuming he'll average 5 PA/G in the postseason, that is 90 postseason PA. So you'll want him to enter the postseason with no more than ( ( 1.1 * Actual PA * (180/162) ) - 90), or (0.95 * Actual PA), whichever is greater. If I did my math right. I should be doing something else right now anyway!

Not that it changes things much, but isn't there a day of rest at the All Star Break, meaning a player actually receives 163/162 PA/162? Is there also a day of rest before the playoffs, and if so is fatigue recalculated before or after that day of rest?

Not sure about All-star break, but I think you are right about a day of rest before the playoffs. For the team I quoted above, I noticed that they had one more day of rest before the next series started. So after winning a best-of-seven series, it was like they were 8 games further into the season when the next series started.