Why freelancers underprice themselves
The usual method is to take a salary, divide by two thousand hours, and quote that. It produces a rate that is too low for three reasons at once. It assumes every working hour is billable, when sales, admin, invoicing and unpaid gaps between clients are not. It ignores the benefits a salary carried - provident fund, gratuity, paid leave, insurance. And it treats tax as somebody else's problem, when a freelancer pays their own.
This page inverts the calculation. You tell it what you want to keep after expenses and after tax; it solves for the gross receipts that produce that, and divides by the hours you can genuinely bill.