The boring stack
Hardware amortization, software subscriptions, professional insurance, accounting, continuing education. Individually small; together typically $6–15k a year. Every dollar belongs in the rate formula as an expense — and most freelancers price it at zero because it never arrives as a single scary invoice.
The invisible benefits package
Health insurance, retirement contributions, and disability coverage are not perks for the self-employed — they are the products your old employer bought in bulk. Price them as expenses and the "2× the employee rate" rule stops feeling like folklore and starts feeling like arithmetic.
The invoice that never gets paid
Non-payment is an expense line with a probability, not a myth. A 2% bad-debt assumption plus clear contracts, deposits on new clients, and late fees keeps it a rounding error instead of a quarterly crisis. Build it in; collect deposits; stop donating work.