Renting my SFH per BR & utilities are split. When/What fee can I charge if unpaid?

[Jill Jay]

Hi BP community! I am renting out my single family home I currently reside in per bedroom. I currently have 2 tenants who are college grads at the local colleges. Their parents are cosigners and pay their rent+utilities. They typically always pay on time but recently the parent didn't pay their portion of the utilities until the following month. This normally wouldn't be a big deal but it was an oil delivery & it was frustrating worrying about whether it would be paid. In the lease it states that utilities are split equally among tenants & myself.

My question is how long are tenants allowed to have before I'm able (if I'm able) to charge a late fee? How much of a late fee am I allowed to charge?

Thank you everyone for your input :)