How do I calculate projections using monthly sales growth?

[Alaina S]

For example, assuming my growth rate is 10% a month and my sales dollars for month 1 is X, how do I calculate how much my projected sales will be per month after 12 months, and the total sales at 12 months? Or 24 months, and so on?

If I have the math right, to see my monthly sales after 12 months at 10% is: (1.1^12)X. Now, how do I find the total sales after 12 months? I'm figuring X+1.1X+(1.1^2)X+ . . . +(1.1^12)X. But this is a lot of long arithmetic, especially projecting several years. There's a calculus solution here but I don't know how to figure it (been too long since college!)

Basically, how do I calculate the series:

x+(yx)+((y^2)x)+((y^3)x)+. . . +((y^n(x))

without breaking my hand? I have a bit of calculus background (calc 1 if I remember?) but not too much...

Please correct any arithemtic mistakes too please!
Thanks!

-mike

[freshwater angler]

wouldnt you just do (1.1^24) for 24 months