Formula
Price = (Hours × Rate + Expenses) ÷ (1 − Margin)
FAQ
Cost rate or billing rate for hours?
Use your internal cost rate to protect margin; the difference between cost-based price and market price is your actual margin. Using billing rate inside the formula double-counts.
How do I handle scope creep?
Define change-order terms before starting. A price is only as good as the scope it assumes.