Compound Interest

Definition of Compound Interest

  • Compound interest is the interest paid on both the principal and the interest you earned so far on that principal.

Examples of Compound Interest

  • Suppose you invested $500 for 4 years in a bank and the bank pays 2% compound interest annually.

By the end of first year, your account balance would be

$500 + 2% of $500 = $500 + $10 = $510.

For the second year, this $510 will be considered as the principal and the interest will be worked out for this amount.

That means, the interest for the second year will be calculated on the principal $500 and the interest $15.

The same process will continue for 4 years.

 

Solved Example on Compound Interest

Charlie deposited $1,000 for 3 years. The bank pays 3% compound interest annually. Find the balance in the account at the end of 3 years. Use a table to calculate the compound interest.

Choices:

A. $1,092.73

B. $1,047.89

C. $1,085.69

D. $1,023.58

Correct Answer: A

Solution:

Step 1: The balance in the account is equal to the sum of the principal and the simple interest.

Step 2: The rate of interest is 3% = 0.03.

Step 3: To calculate the compound interests for three years, make a spreadsheet as shown below.

Principal at the beginning of each year
Interest
Balance
Year 1: $1,000.00
1,000.00 × 0.03 = 30
1,000.00 + 30 = 1,030.00
Year 2: $1,030.00
1,030 × 0.03 = 30.90

1,030.00 + 30.9 =

1,060 .90

Year 3: $1,060.90
1,060.90 × 0.03 = 31.83
1,060.90 + 31.827 = 1,092.73

Step 4: So, the balance at the end of 3 years is $1,092.73.

Related Terms for Compound Interest

  • Rate of Interest
  • Principal

Real-world Connections for Compound Interest

  • The concept of compound interest is used in banks and many finance companies.
 

Additional Links for Compound Interest