Your real minimum viable rate — after taxes, benefits, downtime and business costs.
What you need to charge to actually make it work
The most common mistake freelancers make is comparing their hourly rate to an employee's hourly wage equivalent without accounting for the difference: employees get paid holidays, sick leave, employer National Insurance/payroll taxes, health insurance contributions, and don't need to spend time on admin, marketing, or unpaid proposal work.
A realistic billable percentage is 50-65% of working hours for most freelancers — the rest goes to admin, business development, invoicing, and professional development. Someone working 40 hours a week might bill 20-25 hours. Your rate must cover all the non-billable time too.
Self-employment taxes add roughly 15% on top of regular income tax in the US (or equivalent in other countries) — often forgotten when setting rates because it doesn't appear as a paycheck deduction in the same obvious way employer payroll taxes do.