How to customize crm contact entity

Hello All,

I have setup dynamic CRM in O365. Now i want to add 200+ contacts in CRM. I have one typical scenario here. I want to maintain last 4yrs financial details  for all the contacts. How to customize  contact entity for this. I want to know how to create a column for Fy year (I know how to create a custom column in crm but here This number updates each year.  May want to allow for multiple entries for previous years in order to show history of data.) How to do this.

Thanks