I don’t think its necessary to take into account bodyweight on the major lifts, including squats. The vast majority of lifters, including those the advocate RM type planning, don’t. There are a few exeptions, however. Weighted dips and pullup are two. The added weight probably represents less than half, and sometimes only a fraction, of the total load. If you hang 50lbs. around your waist for a 1RM dip, and you want to work at 85%RM, doing dips with 42.5#s on your belt won’t be correct. If you weight 150, your 1RM is 200 (body weight plus extra weight. So 85% is really 170, which is bodyweight plus 20.
Again, I don’t know anyone personally who uses this calculation for any lifts other than dips and pullups.