I read a lot about 5 and 6 trips a month but at 900 hours a year one can fly 75 hours a month so I fail to see how you do 5 or 6 LH trips a month unless you are flying 6 hour legs.
It’s 900 hours over 10.5 months as you get four weeks of leave and two “duty free weeks” (which are broadly the same thing), meaning 85 hours per (worked) month. However, we work on credit hours not flown hours. The annual total target credit hours on longhaul is 1055 (I think), which also includes a credit hour value for leave, sims, etc. It’s no coincidence that when the leave credit, sim credit and so on are removed, the answer gets very close to 900 and as most trip credit is flying hour based (long trips of which there are few are calculated slightly differently), you need to average 85 flying hours per month worked.