A lease extension addendum is added to an expiring lease to add terms that prolong the lease past the original end date. This allows the original lease to be extended by adding a date that is further into the future or by amending it to be a month-t0-month lease. In either option, the tenant is able to stay on the property. Unless modified, all other terms and conditions of the original lease will be enforced during the extension period including the monthly rent.