Help - how to create a variable that determines how many months of data get manipulated

[clanger32]

hi,
I am trying to create a model in which a given volume of data is added on a month by month basis, but after a variable period, some of that data will be deleted out.
so the extract looks basically like this (very small excerpt):
Monthly 1 2 3 4

Data added 50.00 50.00 50.00 50.00
total Volume - 92.50 180.38 263.86

The row "total volume" is (here) adding the second months volume of data to that received in the first month and then is applying a 5% reduction. The 5% reduction is one variable which is user defined and references how quickly you can deal with the data and get rid of it.

My challenge and what I would be very grateful for help on, is that I'd really like to create a user defined variable that defines how many months it takes to DEAL with that data - here it's hard coded by changing the formula the requisite number of months later on to include a subtraction value. Clearly that's "ok" for a situation in which everyone agrees that you can be finished with the data in a set time, but it's virtually impossible to allow for a "what if" situation.

Ideally, I'd have something that says (in plain English, rather than TRYING to write it in excel-ese) "Row 3 is the amount of data coming in, each month. Row 4 should be the aggregated total of the data added in every previous month, to give a rolling total, but should delete a variable percentage, x many months after receipt, where x is a user defined variable"

any thoughts?
thanks

[AliGW]

Welcome to the forum.

The LET function allows you to define variables in a formula.

There are instructions at the top of the page explaining how to attach your sample workbook (yellow banner: HOW TO ATTACH YOUR SAMPLE WORKBOOK). Screenshots are of little practical use as we cannot manipulate them.

A good sample workbook has just 10-20 rows of representative data that has been desensitised. It also has expected results mocked up, worked examples where required, relevant cells highlighted and a few explanatory notes.