Match the deposit to the engagement
Consider the project length, up-front costs, client history, cancellation risk, and how much capacity you must reserve. A small repeat engagement may need less protection than a custom project that blocks several weeks.
The percentage matters less than whether the payment schedule keeps your exposure reasonable throughout the project.
Explain what the deposit does
State that the deposit reserves the planned start window and authorizes initial work. Identify any third-party costs that must be paid separately before purchase.
Describe cancellation and refund treatment in language appropriate to your agreement and jurisdiction. Get professional advice when the amount or risk is material.
Make the next payment predictable
Show the remaining balance beside the deposit. Tie it to delivery milestones or a dated schedule so the client can plan.
Do not wait until final delivery to discuss an overdue milestone. Use the pause rule in the scope consistently and document any exception.