Calc Linear curve with data points

[maccritter]

I’m trying to calculate the data points from a given decline curve. If I know I’m starting out with a number such as 3200 and this number will decline 65% over 12 months, how do I have Excel plug in the 12 data point values in a linear or even a non-linear decline curve. In reality the curve is non-linear meaning that the decline is more rapid in the first 3 months than it is in next and successive 3 months ending with a total decline of 65% from the original value of 3200. However, if there is not an easy way to determine the non-linear curve, then for my purposes a linear decline would be ok.
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To summarize, my variables might look like the following ….
· 1<SUP>st</SUP> month IP = x (3200)
· 1<SUP>st</SUP> year decline = y1 % (60%)
· 2<SUP>nd</SUP> year decline = y2 % (75%)
· 3<SUP>rd</SUP> year decline = y3 % (85%)
· 4<SUP>th</SUP> year decline = y4 % (90%)
· 5<SUP>th</SUP> year decline = y5 % (92%)
· 6-10 year = y6 % (93%)
· 11-20 year = y7 % (94%)
· 21-30 year =y8 % (95%)
· Etc.
The result of the equation should fill out an array of cells with the actual data values for each month within that time period.
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I would like to be able to change the starting value and/or the decline rate percentage and have the spreadsheet re-calculate the data points.

I'm hoping there might be a built-in formula for this, but if not would welcome any ideas.

Thanks