Personal training used to be a cash business. Clients would turn up, get sweaty for an hour, and hand over a bunch of wrinkled £20 notes at the end of the session. Or crumpled $20 bills, if you’re into that sort of thing.
Maybe you’ll hand over an invoice or receipt, but probably not. Maybe you’ve got a safe in the office for all that cash your collecting, but it chances are it just lived in your wallet for a few hours until you got home.
When you’re done training clients it’s time to switch off PT mode and start getting comfy as a DIY accountant, updating your messy spreadsheet with ins and outs and cashflows and expenses and all sorts of numbers you never really intended to master when you qualified as a personal trainer.