Not what feels fair — what actually gets you to your income goal, after tax and after expenses.
This is a different question than "what do I owe" — that's what the free tax calculator answers. This one works backward from what you want to take home.
This calculator is one piece. The full Freelancer Money Kit adds a one-page profit & loss template you can hand to a lender, plus account structures built for your specific kind of business — not business in general.