Operating costs

Anybody mind giving their 2 cents on how to factor their accesorial CPM being that permits and escorts are highly variable costs on this side of things? I’ve got a notebook I kept where the actual CPM varied from 1.80/mi up to 3.67/mi on some of the heavy escort loads. For fuel I just used my average mpg at my heaviest weight figuring that would give me wiggle room for the times I’m lighter or legal. Thanks in advance