Want to have a survey regarding late fee

I saw different version of late fee charges in lease agreement. Some charges $20 per day, others charge $40 if not paid by 5th, and additional $30 if not paid by 6th. Not sure how you guys handle the late fee in the lease, as well as the actual amount you charged. Is there any limit on the late fee that you can charge? Hope you can share some idea on this.