My understanding of the total months difference between 2 dates has an integral and a fractional part (the date matters). The integral part is the full months difference. The fractional part, for me, is the difference of the % of the day (to the full days of month) between the starting and ending months.y understanding of the total months difference between 2 dates has an integral and a fractional part (the date matters). The integral part is the full months difference. The fractional part, for me, is the difference of the % of the day (to the full days of month) between the starting and ending months.