Interest is the money paid for the use of borrow money. It is calculated as a percent of the principal.

For example, suppose that you deposit $100 in a bank account offering 10% interest, how will your money grow in one year?

**Answer**: The total amount would be $110, the original principal plus the interest (10% of 100 = $100(0.10) = $10).

There are two types of savings accounts:

**Simple interest**accounts (the interest earned is paid to the depositor)**Compound interest**accounts (the interest earned is left on deposit to earn more interest

**Interest**

### Simple Interest

Simple interest is the most common type of interest on loans for a car.

This type of loan is usually used for short-term loans.

Simple interest is determined by multiplying the interest rate by the principal by the number of periods. **I = p r t**

Example: How much we will get by investing **$100** for **2 years** with a bank that pays **10%** (simple interest rate) annual?

The total amount would be **$120**, the original principal ($100) plus the interest (100*0.10*2) = $20).

The future value is the present value plus the interest.

Future value = principal + interest = p + I

Compound Interest Formula

F = Future value

P = Present value (Principal)

r = annual interest rate

n = number of compounding periods

t = time (years)

**Interest on Interest**