Some states that do regulate LATE RENT FEES may also state that a LATE FEE may not be charged until 5 or 10 days (or any number) after the due date or not until the tenant is notified, in writing, of the rent due and possibility of being charged a late fee. You may also give the tenant 3-5 days (if you choose) BEFORE you decide to charge a late fee.
If you accept late rent payments from the tenant, even with the late payment fee, you may be telling the tenant "it's ok to pay late" - this is what you
"imply" to the tenant.
While it does no good for the tenant to pay late rent, especially with the late fee, some do.
As a landlord, be sure ONCE THE FIRST PAYMENT IS RECEIVED LATE, CHARGE A LATE FEE.
Do so in a standard letter, delivered Certified Mail. Be sure your late fee clause in contained in WRITTEN LEASE and be specific WHEN and HOW MUCH the reasonable late fee will be if rent is not paid on the DUE DATE.
Often what happens when a tenant is late in paying rent, YOU as the landlord wind up becoming late on your payment for related bills, especially if your rental income does not cover your operating expenses.
Different rules may apply for Federal or State subsidized housing. Read your contracts you sign with the Federal or State Agency to understand if and how much you can charge for late rent payment fees.
