When can I charge a late fee?

[Jacob Casarez]

I currently rent out 3 rooms in my home. I have a rental agreement with each tenant-roommate that says when rent is due. Can I Iegally charge late fee per day if rent is not collected? Obviously I would get that in writing on the agreement -- But I ask this question because I heard once about there being a legal 5 day grace period..is that true?? Please help, BP Thanks!