Compound Interest

Compound interest is the interest on a loan or deposit calculated based on both the initial principal and the accumulated interest from previous periods. Unlike simple interest, which is calculated only on the principal amount, compound interest grows exponentially over time because it includes interest on the interest already earned.

Key concepts of compound interest


The principal is the original amount of money invested or borrowed. This is the base amount on which interest is calculated.

Interest rate

The interest rate is the percentage at which the interest is calculated on the principal and the accumulated interest. It is typically expressed as an annual percentage rate (APR).

Compounding frequency

Compounding frequency refers to how often the interest is calculated and added to the principal. Common compounding frequencies include annually, semi-annually, quarterly, monthly, weekly, and daily. The more frequent the compounding, the greater the amount of compound interest.


Time refers to the duration for which the money is invested or borrowed. The longer the time period, the more compound interest will accumulate.

How compound interest works

Compound interest is calculated using the formula:

A = P (1 + r/n) nt


  • A is the amount of money accumulated after n periods, including interest.
  • P is the principal amount (the initial amount of money).
  • r is the annual interest rate (decimal).
  • n is the number of times interest is compounded per year.
  • t is the number of years the money is invested or borrowed for.

Example calculation

Consider an initial investment (principal) of $10,000 with an annual interest rate of 5% compounded annually for 5 years.

Using the formula: 

A = 10,000 (1 + 0.05/1) 1 x 5

A = 10,000 (1 + 0.05) 5

A = 10,000 (1.05) 5

A = 10,000 x 1.27628

A = 12,762.82

After 5 years, the investment will grow to $12,762.82, with $2,762.82 earned as compound interest.

Benefits of compound interest

Exponential growth

Compound interest grows exponentially over time, meaning the longer the money is invested or borrowed, the more significant the growth. This makes compound interest a powerful tool for building wealth over time.

Higher returns

Due to the compounding effect, investments with compound interest often yield higher returns compared to those with simple interest, especially over long periods.

Incentive to save and invest

Understanding the power of compound interest can motivate individuals to save and invest early, taking advantage of the exponential growth potential.

Compound interest in various financial contexts

Savings accounts

Many savings accounts offer compound interest, allowing account holders to earn interest on their deposits over time. The frequency of compounding can vary between daily, monthly, or annually, affecting the total interest earned.


Compound interest plays a crucial role in investment vehicles such as mutual funds, stocks, and bonds. Reinvesting dividends and interest payments can lead to significant growth in the value of the investment over time.


For loans, compound interest means borrowers may end up paying more over the life of the loan compared to simple interest loans. It is essential for borrowers to understand the terms of their loans, including the interest rate and compounding frequency.

Retirement accounts

Retirement accounts, such as superannuation in Australia, benefit greatly from compound interest. Regular contributions and compound interest over a long period can significantly grow the retirement savings.

Example of compound interest in real life

Consider an individual in Newcastle who starts investing $5,000 annually in a superannuation fund at the age of 25 with an annual interest rate of 7%, compounded annually. They continue this investment until they retire at age 65.

Using the formula for the future value of a series of cash flows: 
FV = P ( (1+r)n-1 / r )


  • FV is the future value of the investment.
  • P is the annual payment ($5,000).
  • r is the annual interest rate (0.07).
  • n is the number of years (40).

FV = 5,000 ( (1+0.07)40-1 / 0.07)

FV = 5,000 ( (1.07)40-1 / 0.07 )

FV = 5,000 ( 14.974-1 / 0.07 )

FV = 5,000 ( 13.974 / 0.07 )

FV = 5,000 (199,628)

FV = 998,140

By the time they retire, the investment will have grown to $998,140, showcasing the power of compound interest over a long period.


Compound interest is a fundamental concept in finance, offering significant benefits through exponential growth over time. Whether saving, investing, or borrowing, understanding how compound interest works can help individuals make informed financial decisions and maximise their returns. For more information on compound interest and its applications, you can visit the Australian Securities and Investments Commission (ASIC) website.

DISCLAIMER: The information provided on this page is for general informational and educational purposes only and is never intended as financial advice. While we strive to ensure that the content is accurate and up-to-date, it may not reflect the most current legal or financial developments. Always consult with a qualified financial advisor or professional before making any financial decisions. Use the information at your own risk.


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