Do my unused leads roll over to next month?

Yes. While your plan is active, any leads you have not used stay on your account. Each month's leads are added to what is already there rather than replacing it, so nothing expires while you are subscribed.

If your plan ends

Nothing is deleted. The leads you had left are kept on your account and come back the day you start a plan again. Top-up leads you bought stay usable in the meantime, for 12 months from the day you bought them, oldest first.

Trial leads when you start a plan

Any free trial leads you have not used stay on your balance when you start a plan, alongside the plan's leads.