# Thread: Calculation problems for Annuties and Interest

1. ## Calculation problems for Annuties and Interest

Going off this site

The Present Value and Future Value of an Annuity; Annuity Due, Ordinary Annuity; Time Value, with Formulas and Examples; Discount Rate

I am trying to figure out how annuities and interest works.

So I decided to Calculate this:

100 * ((1+.005)120 -1)/.005

FVOA =

A * (1 + i)n - 1 / i

A= Amount
i= Interest
n= number of periods

According to the website the answer is $36,387.93 But when I put it in on my calculator, the answer is$16,387.93

My answer is exactly $20,000 less than the answer the site gives. Any reason for this? 2. They made a mistake. According to their formula, your answer is correct. 3. According to the website, the formula for the future value of an annuity is$\displaystyle FVOA = \frac{A[(1 + i)^n - 1]}{i}$. You multiplied$\displaystyle (1 + i)$by$\displaystyle n$instead of raising$\displaystyle (1 + i)$to the$\displaystyle n$th power. 4. Originally Posted by NOX Andrew According to the website, the formula for the future value of an annuity is$\displaystyle FVOA = \frac{A[(1 + i)^n - 1]}{i}$. You multiplied$\displaystyle (1 + i)$by$\displaystyle n$instead of raising$\displaystyle (1 + i)$to the$\displaystyle n\$th power.
NOX, I tried by raising to n (I did go onto the website to check) and it yields the same result. They indeed made a mistake.