Inventory Aging report

Hello,

I have to create an inventory aging report with FIFO in mind but not sure what formula will work the best. I have the purchases and sales for 4 months, starting from April through September. From the April purchase, April sales needs to be deducted and the inventory remaining should be added to the new purchase. For May, the total inventory after sales should show how many from the April (which is now 30 days old) and the may inventory remaining. The trend should keep going on, any sort of help will be greatly appreciated.

Purchase Sales QOH 0-30Days New
April 40 10 30

May 20 5 45 25 20