Nearly every rate calculator assumes you bill every hour you work. You don't โ nobody does. This one starts from the take-home you need and prices in the hours you'll spend on everything that isn't billable.
Treat the hourly figure as a floor, not a price. It is the number at which you break even on the life you described โ quoting at exactly this leaves nothing for a bad month, a client who pays late, or a project that runs long. Most people should add margin on top and quote fixed-price where they can.
This is the slider that matters most, and the one every "salary รท 2080" calculation ignores. Sales calls, invoicing, unpaid scoping, admin and the gaps between contracts are all real hours that no client pays for. Assume 80% and you will quietly earn a fraction of what you planned.
Tax handling here is a simplification: it applies one effective rate to profit after expenses. Real brackets, deductions and local rules vary โ use this to size the rate, not to file anything.