Crystal Report : Count days

Hello Experts,

I need to develop ageing report for my stock.
I have issue to count the ageing and grouping .
The report shall calculate aging using the download date - stock date .
then I need group it in column aging

example : < 30 days , < 60 days , < 180 days

when stock aging is 61 days , the stock value and quantity will print at column 60 days.

Can share your experience with me ? :)

Thank you