Compound Interest and Rule of 72

Understanding Compound Interest

One of the fundamental money concepts is Interest.

Interest, to give a very basic example, is often a “price” that is paid to borrow money. Compound interest is when interest is added to the starting amount, or principal, so that the interest that has been added also earns interest.

With compound interest, you earn interest on the money you save and on the interest that money earns. Over time, even a small amount saved can add up to big money. Whether you realize it or not, the concept of interest is a big part of your financial life because the possibility of earning interest is why people lend and borrow money.

What Does This Mean?

Your money can work for you when “your money earns money”. When your money goes to work, it may earn a steady paycheck. Someone pays you to use your money for a period of time. When you get your money back, you get it back plus “interest.” Your money can make an “income,” just like you. You can make more money when you and your money work.

The Rule of 72

The Rule of 72 is a mathematical formula used to estimate the amount of time it would take for an amount to double using Compound Interest.

This formula is very useful because it helps you estimate how much time you need and what kind of interest rate you need to reach your financial goals.

The Rule of 72 Formula: Divide The Interest % Into 72 To Estimate The Number Of Years To Double Your Principal*

Your Money Working For You

This example shows how compound interest can work in your favor by doubling your money after a certain number of years depending on the interest rate you are earning on your principal.

We can use the Rule of 72 to calculate the amount of time required.

72 / 4% = 18 Years To Double

72 / 8% = 9 Years To Double

All figures are for illustrative purposes only.

*This is a hypothetical scenario used for illustrative purposes and does not reflect the results of any specific investment. The actual time it will take an investment to double in value cannot be predicted with absolute certainty because performance of investments fluctuate over time.

Compound Interest Can Work Against You

Just like you can earn interest on money you have, banks and other financial institutions lend you money to earn interest.

Here is an example of how compound interest works against you.

Credit Card Debt

If You Have A $3,000 Credit Card Balance At A 19% Annual Interest Rate, And You Only Pay The Required Minimum Balance Of 2%…

How Many Years To Pay Off The Card?

At Least 30 Years**

How Many Payments?

Over 720 Payments**

How Much Will You Pay In Interest?

More than $8,500 in interest alone**

All figures are for illustrative purposes only.

**Source: Credit Card Repayment Calculator, available at

Read More About Money Concepts

Find out why it is crucial to counteract the effects of inflation.

Please note: The material on this website is intended for informational purposes only. Neither Syncis, LLC nor its affiliate companies authorize its agents, employees or representatives to give legal, tax or accounting advice. Please consult the appropriate professional for legal, tax, or accounting advice.