Plan 17 off for a line and 15 off for reserve. You'll get more off on a line but 17.3 is our average. 20 off being on the high side. There are also ways to manipulate you schedule by how you bid. Conflicts from monthly overlap help, but you can also get hosed by scheduling so you have to know what you're doing.
This month with 1 week vac and monthly overlap I got 28 days off and pay of 64. I got lucky and did some extra flying so I'll end up with 22 off and pay of 131. Best ratio I've ever had. 4 yr FO at sw