Yeah, everyone has different formula; I was told this one:
(Cycle + PCT) X2= time off tough in that formula pct time is same time as cycle time- tough last pct part includes little bit of test boosters or vitamins, further liver "cleansing"

anyway for average longer cycle it comes as: (13 + 13) x2= 26 so if we add all this together we get 26+26= 52 weeks which is a year, so it means one cycle per year (or two shorter)