
Calculation of Interest
Hi all, was wondering if someone could help me in solving this formula:
I want to add a certain percentage of interest to a capital amount for a certain number of months. I don't know how to calculate the formula. remember the capital amount will be growing every month.
Example: Capital = 1000 Interest = 5% Months = 3
1000 + 5% = 1050
1050 + 5% = 1102.50
1102.50 + 5% = 1157.62
What would the formula for this be if Capital was X, Interest was Y and Months where Z?
Please guys I really want to use this formula in a Excel spreadsheet
All Help appreciated!

Unless I'm misunderstanding something you can use the compound interest formula:
$\displaystyle P(t) = P_0 \left(1+\dfrac{r}{n}\right)^{nt}$
where:
 $\displaystyle P_t$ = amount at time t
 $\displaystyle P_0$ = initial/principal
 $\displaystyle n$ = number of annual compounds (if you're compounding monthly it's 12)
 $\displaystyle r$ = annualised rate (APR)
 $\displaystyle t$ = time
In your case you can simplify to $\displaystyle P_t = P_0(1+r)^t$  but set r to the monthly rate (5%) and t to months