Monthly / Yearly rents keep billing automatically — from the
Start Date, one more rent amount is added to the due every period, so it has to be paid every
month (or year). Set an End Date to stop it; leave empty to run indefinitely.
A monthly rent is charged by days in its first and last month — from the Start
Date to that month's end, and from the 1st to the End Date — and in full for every month between.