Fill Data Based On Date Calculations

I am having problems with calculations to be performed on date format. As in attached excel sheet, Start Date and End Date can be defined by the user. Once the user enters the dates, year 0 onwards are to be populated with values so that: (Also, not sure if I will need a button to initiate the calculations or a direct function will suffice)

year0 start = Start Date,
year0 end = (Start Date +12 months) or (End Date), if End Date is before (StartDate + 12)

year1 start = year0 end,
year1 end = (year0 end + 12 months) or (End Date), if End Date is before (year0 end +12)

year2 start = year1 end,
year2 end = (year1 end + 12 months) or (End Date), if End Date is before (year1 end +12)

year3 start = year2 end,
year3 end = (year2 end + 12 months) or (End Date), if End Date is before (year2 end +12)

year4 start = year3 end,
year4 end = (year3 end + 12 months) or (End Date), if End Date is before (year3 end +12)

year5 start = year4 end,
year5 end = End Date

If the dates are such that all years 0 to year 5 may not be covered, the years not used should be blank.