Inventory Formula

[Rameau]

Hello - I'm trying to find a formula that would allow me to perform the following calculation:
The average number of new consumers is x per location per month
The current level of goods = y
By dividing y/x = the lifespan on a monthly basis
If I need to determine the number of lifespan unit to get me to let's say 5 month what would be the formula?

Ex: 2 new consumers per month
Current level of goods = 4
Lifespan = 2 (missing 3 lifespan)

Also I need the formula to generate a "0" if I already have enough inventory for the timespan indicated.

Thanks.

 

[Rameau]

Hi - Just following-up. Any help would be appreciated. Thanks.