If you’re looking for a simple way to teach your homeschool kids about investing, interest, and how money grows, the “Rule of 72” is a perfect place to start! It’s an easy math shortcut that helps you estimate the number of years it will take for your money to double at a fixed annual rate of return or interest rate.
What Is the Rule of 72?
The formula is simple:
72 ÷ rate of return = years to double your money
For example:
If your investment earns 6% interest, you can calculate:
72 ÷ 6 = 12 years
That means it will take about 12 years for your money to double.
If the interest rate is higher, your money grows faster. If it’s lower, it takes longer to double.
You can also use this handy equation to figure out the rate of return you need if you want your money to double in a certain number of years.
For example:
If you want your money to double in 10 years, what rate of return would you need?
72 ÷ 10 = 7.2, so you’d need an investment earning a 7.2% annual rate of return.
It’s important to know that the of 72 is a quick shortcut formula. It’s meant to give you ballpark estimates and is not 100% accurate.
Why Teach Kids This?
This rule helps kids understand some key investing concepts:
- The power of compound interest – how money can grow over time without them adding anything extra.
- The risk-return trade-off – how a higher rate of return can help our money grow faster.
- It also helps them see why starting early with saving and investing is so important. Proverbs 21:5 reminds us: “The plans of the diligent lead to profit as surely as haste leads to poverty.” When we’re wise and diligent with money, time becomes our friend.
Fun Homeschool Activity: Double It!
- Pick an interest rate (for example, 4%, 6%, or 8%).
- Have your child use the Rule of 72 to figure out how long it takes to double the money.
- Make a chart showing how $100 would grow over time at that rate, doubling at each step.
- Challenge them to try different interest rates and see how much faster or slower the doubling happens.
This is a great way to mix math, economics, and Biblical stewardship in your homeschool lessons.
Download a free Rule of 72 worksheet!
