Who this is for
Fixed-fee projects create a billing problem hourly work never has: each invoice is a fraction of an agreed total, so every document must answer three questions at once. What is the full price, how much has been billed so far, and what remains? Invoices that answer only 'what do I owe now' generate end-of-project reconciliation disputes almost by design.
Use this calculator to structure deposit, milestone, and final invoices that carry the running math. The guidance covers milestone definitions clients cannot argue with, change-order separation, and the final invoice that closes the project at exactly zero balance.