The most common model, followed by most of the big registrars, is up to 45 days for normal renewal, but some registrars charge more before the 45 days is complete, then on the 46th day the domain is given back to the registry for a 30 day Registry Redemption Period, then it goes into Pending Delete for 5 days when nobody can renew it. Then on the 6th day it drops. 45+30+5+1= 81 days. These days are basically set in stone by ICANN. It's only how an individual registrar handles things up to the 45 day mark which differs.
One exception is how 1and1 handle this. They don't give you any renewal period at normal renewal rates and delete the domain after 30 days.