The project's finished, the client's happy, so it made money. Right? Not necessarily. The scariest projects are the ones that felt fine and quietly lost margin.
Every project has two numbers. What you quoted, and what it actually cost you to deliver. The gap between them is your real profit, or your lesson.
You quoted 100 hours at £100 an hour: a £10,000 job.
You actually spent 130 hours.
That's £3,000 of over-servicing. Work you did and didn't charge for.
Over-servicing isn't generosity; it's unpaid work that eats the margin you already earned. A little is normal. A pattern is a problem, and it usually starts with unclear scope or scope creep no one billed for.
When actual beats quoted, don't just shrug. Ask why.
If the scope grew, that should have been a change request and a new fee. If you underquoted, fix the rate card or the estimate next time. If it was inefficiency, that's a delivery conversation. If it was a genuine one-off, note it and move on.
Run a quick post-project review on every meaningful job: quoted vs actual, and one line on why. Do it enough times and your quotes get sharper and your margin stops leaking.