Let's begin with simple interest.
Simple interest is computed only once for the duration of the loan or investment.
Let's say the account pays 5 percent interest. Compound interest is calculated more often, and as soon as it is calculated, the interest in added to your account. That way the next time the interest is computed, you have MORE in your account than the money you put there. We can use the Simple Interest formula over and over to figure your interest. Add it to your account.