[pushplay]

If you're managing your project in a tool like JIRA you could provide your client with a burn down chart. It's the easiest way to tell at a glance how a project is going, and takes next to no effort to produce.

If you're not managing your project in such a tool then you should be. If you're not breaking your job into small enough tasks that the chart looks reasonable then you should be doing that too. Both these things will force you to come up with better estimates and give you a record to learn from to provide better records in the future.