Holding Period duration

[subrat1]

I wanted to calculate holding period of mutual fund, If the quantity is sold in any month then the program should automatically create a new column called Holding period and  then calculate the difference of duration as shown in below table.

For example for mutual fund no :124, The current month quantity is 3000 and previous month was 4000 that means its sold in this month by 1000 unit.

But if the quantity is never sold like for mutual fund no :236 then it should give the duration from current month till first month.

Mutual Fund	Quantity_201904	Quantity_201903	Quantity_201902	Quantity_201901	Holding Period_1	Holding Period_2
124	3000	4000	1500	2000	1	2
236	4000	3000	2500	500	3	0
456	7000	4000	3500	800	3	0

[Astounding]

What if there are choices to be made?  For example:

January:  1000

February:  2000

March:  3000

April:  2000

The 1000 that were sold in April could come from any of the previous three months that were all purchases.  What should the holding period be?

What if the pattern looks like this:

January:   1000

February:  3000

March:  5000

April:  3500

May:  2000

What's the holding period for May, when the 1500 that were sold were purchased during more than one month?