This is a junior P2 747 roster from a recent month............
Day 1 Off
Day 2 BOM 4 day trip
Day 6 Off
Day 7 Off
Day 8 CPT 5 day trip
Day 13 Off
to
Day 16 GRU 5 day trip
Day 21 Off
to
Day 24 PEK 4 day trip
then off to end of month.
Thus 18 days work in a 30 day month but only 81 hrs 15 mins credit hours.
So if this pilot wasn't on a blind line he would have needed hours in the bank to avoid losing money from his pay packet.
Main point to note is this was chosen at random and there are other less desirable combinations.....