Finally, once you’ve gotten all your expenses filled in, add 15% for expenditures you haven’t counted yet. Yes, really. For example, you probably didn’t capture “car repairs”, which can cost £400 each time (that’s £33/month). Or dry cleaning or emergency vet care or charitable donations. A flat 15% will likely cover you for things you haven’t figured in, and you can get more accurate as time goes on.
