How do you calculate the balance in an account, with interest?

Divide your interest rate by the number of payments you'll make in the year (interest rates are expressed annually) ...

Multiply it by the balance of your loan, which for the first payment, will be your whole principal amount.

Step-by-step explanation:

The ending balance, or future value, of an account with simple interest can be calculated using the following formula: Using the prior example of a $1000 account with a 10% rate, after 3 years the balance would be $1300. This can be determined by multiplying the $1000 original balance times [1 + (10%) (3) ], or times 1.30.