It's not rocket science. You have to experiment, and let your body tell you. I have a hilly route, and in the winter the issue isn't being warm enough (that's easy), but being cool enough that I don't sweat and wet my insulation on the climbs. I try to start cool, and warm up on the ride.

Since the weather changes gradually usually), I can learn as I go a few degrees at a time. Otherwise, I just add enough and see what happens. Actually, my biggest issue is large temperature swings during the day, where I might go to work correctly dressed for 40° and get surprised having to ride home at 25°,

If you're new to it, don't make yourself crazy, do the best you can and have a bailout. For instance, I can take a bus which gets me within walking distance at either end. If I ride in, and it's pouring, or sleeting in the evening, it's a bus day. (personal rule, I'll ride in the cold, or wet or dark, or even 2 out of 3, but not all three.