Scope creep rarely arrives as one big request. It's a new page here, an extra revision round there, "just a quick change" that turns into a day. Each one seems too small to charge for, but together they can wipe out a project's profit. This calculator prices a change request fairly and shows exactly what doing it for free would cost you.
How it works
Start with the hours the change adds, then add overhead for everything around it: revisiting plans, retesting finished work, and extra communication. 20% is a reasonable starting point; changes late in a project often need more.
The fee is those billable hours × your rate. By default the rate is the one your original quote implies, price ÷ hours, so the change is priced on the same basis as the project. Add a rush premium if the change has to fit the original deadline.
The absorbed rate shows the alternative: the original price divided by all the hours, including the change. That's your real hourly rate if you say yes without charging, and the pay cut is how far it falls.
Put a change-request process in your contract before work starts: every change is written down, estimated and approved before it's built. It keeps the conversation about scope rather than about favours.
A worked example
You quoted $6,000 for a 60-hour website, which is $100 an hour. The client asks for a booking system that adds 12 hours. With 20% overhead that's 14.4 billable hours, so the change costs $1,440 and the new total is $7,440. Doing it for free would drop your real rate to $80.65 an hour, a 19.4% pay cut.
Questions people ask
How do I charge for scope creep?
Treat every change outside the agreed scope as a change request: write down what's being added, estimate the hours including rework and testing, price it at your project rate and get written approval before starting.
How do I tell a client something is out of scope?
Point to the agreed scope, confirm you're happy to do the extra work, and give the price and timeline impact in the same message. Offering options, such as adding it now for a fee or scheduling it as phase two, keeps it positive.
Should I ever do small changes for free?
Occasionally, as a deliberate gesture, and say so: "I'll include this one at no charge." That makes the value visible and sets the expectation that further changes are billable. Silent free work tends to become the norm.
Why add overhead to change hours?
Because a change touches work that's already done. You re-plan, re-test and re-deploy, and there's more back-and-forth. Pricing only the build time consistently undercharges for changes.
What's a change request clause?
A contract section saying that work outside the written scope is estimated and approved in writing before it starts, and billed at a stated rate. It's the simplest protection against scope creep.