Calculate Recurring Cumulative costs

=78*b14*b15

Try:

=SUMPRODUCT(B14*ROW(1:12))*B15

MY apologies because I don't think I was clear before. I need to ask this another way.

I need to be able to calculate a total amount spent over a period of time. There is no table that represents costs. I only have the following three inputs to provide for an equation (three cells worth of data in the spreadsheet):

1 - months (can enter any number)
2 - Storage growth (this is a fixed value at 10GB per month)
3 - Storage hosting fee (this is a fixed value at $1 per GB)

The way this works is as follows:

The first month I add 10 GB of storage. This costs me $1
The second month I add 10 GB of storage for a total of 20GB of storage. This costs me $2
The third month I add 10 GB of storage for a total of 30GB of storage. This costs me $3

Over the course of three months I have spent $6.

In this example the $6 value is the number I need to be able to get out of the equation.

I need a function that will allow me to input the rate of growth, the storage hosting fee and any number of months I want to give me a total amount spent over the variable amount of time.

It's the sum of an arithmetic series:

Amt1 is the amount spent in the first period

AmtN is the amount spent in the Nth period

The total is =N * (Amt1 + AmtN) / 2

If the period-to-period difference is deltaA, then

Total =N * (2 * Amt1 + (N - 1) * deltaA) / 2

You're welcome. Would you please mark the thread as Solved?