Hi @DCrinnion1
Have you tried using Product/Line items to represent the subscription and which are added to the deal? HubSpot has a default ARR property that updates automatically but it is based on line items associated to the deal. You can also add start and end dates on the line item.
Annual recurring revenue (ARR): the total amount of revenue earned annually for this deal. This is calculated based on the term length and values of the recurring line items associated to the deal. If there is no term length, HubSpot assumes a term of 12 months.
Monthly recurring revenue (MRR): the recurring revenue each month for this deal. This is calculated using the values and term length of the recurring line items associated to the deal (i.e., total value divided by the number of months in the term length).