Is it legal to put a daily penalty?

[Sami Gren]

My tenant us asking for a month extension, but to be sure she will move out at that time, I want to put a big daily penalty fee (maybe like $75 per day) for each day she stays more than a month, so I could make sure she is seriously getting out and not just playing around with me, is it legal? (State of new jersey) And what do you think in general..

[Aidan Mulligan]

1) Depends on where you are, every state is different

2) If it is legal in your state it must be in the leasing contract, you can't amend a contract after the fact