How do we charge for design changes the client asked for after sign-off?

Sign-off fixes the scope. Anything the client asks for after that point is extra unless the agreement says it is included. Most disputes start because the studio did the work first and raised the fee later.

Check the agreement for three things: the rate card, the number of included revisions and the rule for approving extra work. If the agreement is silent, a written request and a client reply still help a great deal.

Keep a simple log. Record the date, who asked, what changed and the hours spent. Timesheets made at the time are stronger than an estimate made at the end.

Send the fee variation within days, not months. A short email with the log line and the cost is usually enough to start the talk.