Rule of 72 calculatorRule of 72 calculator

Rule of 72 Calculator & Uses

September 18, 2023
Family Finance

Understanding how your investments grow is crucial, especially for those planning for future financial milestones.

One key concept that makes this easier is the Rule of 72.

With it, you can quickly gauge how long it'll take for your investment to double, given a fixed annual rate of interest.

Want to know how it works?

Let's dive in!

Rule of 72 Calculator

Welcome to the Rule of 72 Calculator!

This simple yet powerful tool helps you understand how long it'll take for your investments to double.

Whether you're starting with a known interest rate or a specific number of years in mind, our calculator can assist.

How to use the calculator:

  1. Choose a Calculation Method: Begin by selecting whether you want to start with the interest rate or the number of years.
  2. Enter Your Data: Based on your choice, input either the interest rate (as a percentage) or the number of years you're targeting.
  3. Review the Results: Once you enter the necessary data, the calculator will instantly display the time (in years) it takes for your investment to double or the interest rate needed to achieve that within your specified timeframe.

How The Rule of 72 Works

The Rule of 72 is a simple formula.

It is used to estimate the number of years required to double an investment with a fixed interest rate.

Another way to look at it is calculating what interest rate you need to get in order to double your money in a certain number of years.

So, how does it work?

How Long Does it Take to Double with My Interest Rate?

If you know the interest rate your money is earning, you may be wondering how long it will take for your money to double.

You can use the rule to figure out how many years it will take.

The Idea:

Take the number 72 and divide it by your interest rate.

The answer gives you a rough idea of how many years it will take for your money to double.

Let's Try It:

Imagine your savings account gives you a yearly interest of 6%. To see how many years it will take for your money to double:

Years to double = 72 ÷ 6= 12 years

This means with a 6% yearly interest, your money will double in about 12 years.

The reverse also works. Let's take a look.

What Interest Rate Do I Need to Double My Money by my Goal Year?

If you have a goal to double your money in a certain number of years, you can use the Rule of 72 to find out the interest rate you'd need.

It's a great way to set a target for your savings or investments.

The Idea:

Take the number 72 and divide it by the number of years in which you want your money to double.

This will give you the interest rate you'd need.

Let's Try It:

Let's say you want to double your savings in 7 years.

To find out the interest rate you'd need:

Interest rate required = 72 ÷ 7= 10.29%

So, to double your money in 7 years, you'd need an investment or savings account that offers a yearly interest of about 10.29%.

Here's how the rule breakdowns:

Interest Rate Years Interest Rate Years
1% 72 9% 8
2% 36 10% 7.2
3% 24 11% 6.5
4% 18 12% 6
5% 14.4 13% 5.5
6% 12 14% 5.1
7% 10.3 15% 4.8
8% 9 16% 4.5

Common Uses

The Rule of 72 isn't just a mathematical curiosity; it's a real tool people use in their financial lives.

People often turn to this rule when thinking about their savings or investments.

It provides a quick and easy way to visualize the power of compound interest.

Doubling Over Time

With the rule, you can see how quickly your money can double, and then double again, and again.

This repeated doubling can turn even a small amount into a substantial sum over time.

A great real-world example is Warren Buffett. He didn't become one of the wealthiest individuals overnight.

Instead, he consistently grew his wealth, doubling his net worth again and again over the years.

Starting Now Matters

The Rule of 72 highlights an important reality: most investments still take a few years to double your money.

For instance, even at a 10% return, it would still take roughly 7 years to double.

By beginning early, you gain access to many more doubling periods throughout your life.

The sooner you start, the more time your money has to grow.

Overall, many use it as a rough gauge to decide on investment avenues or to set savings targets.

After all, who doesn't dream of their money working for them?

Rule of 72 Examples

Let's see how the Rule of 72 works in real-life situations.

Seeing it in action in everyday scenarios can help you get a better idea of how it works.

1. Child's UTMA Account

Imagine you open a UTMA account for your child and get a 12% interest rate each year.

Using the Rule: 72 ÷ 12 (%) = 6 years.

So the money in that account will double roughly every 6 years.

If you start with $1,000 when the child is born:

Year 6: $2,000

Year 12: $4,000

By the time your child is 18, if you only put in that initial $1,000 and left it alone, they'd have a nice little nest egg thanks to that interest!

2. High-Yield Savings Account

Let's say you find a savings account that offers a 4% interest rate.

Using the Rule: 72 ÷ 4 (%) = 18 years.

So your money would double about every 18 years.

Even with a modest 4% interest, time works its magic, and your savings grow.

However, compared this doubling rate is slow compared to other investment options.

If your goal is to grow your money and make it work for you and your kids, you may want to look at alternative ways to put your money to work.

3. Investing in the S&P 500

The stock market can be a powerful tool for growing money over the long run.

The average return for the S&P 500 in the last 30 years is roughly 10%.

Using the Rule: 72 ÷ 10 (%) = 7.2 years.

If you start investing with $5,000 and the returns stay within the average ranges:

  • After 7.2 years: $10,000
  • After 14.4 years: $20,000
  • ... and so on ...
  • After 50.4 years: $640,000

That's more than a 100X growth!

It might seem surprising, but with time and consistent returns, your initial investment can grow many times over.

This example shows the importance and benefits of starting young.

Setting this money aside in your 20s will get you great returns just in time for retirement.

Investing money for your kids is a solid strategy in building generational wealth.


The formula for the rule of 72 is pretty simple:

T = 72 / I

Spelled out:

Time to Double = 72 ÷ Interest Rate in %

It also works in reverse:

Interest Rate in % = 72 ÷ Time to Double

With this formula you can find out the approximate number of years required to double the money at a fixed annual rate of compound interest.


Time to Double: How long it will take for your investment or savings to double.

Interest Rate: The percentage growth rate at which the investment grows annually.

It might seem almost too easy, but that's the beauty of this rule!

The key takeaway here is that higher interest rates will make your money double faster.

Now, let's put it to the test with an example:

Imagine you're considering an investment that promises a 6% annual return.

To find out approximately how long it would take to double your investment at this rate, you'd use the Rule of 72:

Years to Double = 72 ÷ 6 = 12

So, at a 6% annual return rate, you can expect to double your investment in about 12 years.

Rule Accuracy

While it's a cool tool to have in your financial toolkit, it's essential to understand where it shines the brightest and where it might need some tweaking.

Ideal Range

The Rule of 72 tends to work best for most common interest rates, ranging from 4% to 20%. Within this spectrum, it gives a relatively accurate estimate of the time required for your money to double.

Adjustments for Lower Rates

For very low rates, like 1%, 2%, or 3%, a slight variation called the "Rule of 70" is often recommended. This adjusted rule provides a more accurate estimation for these specific rates.

Higher Rates Anomaly

Taking a look at one extreme case shows the rule's limits.

Take a look at an interest rate of 72%.

Based on the Rule of 72, you'd think your money would double in just a year.

However, 72% is not the same as 100%.

So, in reality, your money would grow by 72%, not double.

Additional Questions

How do you calculate the 72 rule?

The Rule of 72 helps guess how long it'll take to double your money.

Just take 72 and divide it by your interest rate.

The result tells you approximately how many years it'll take for your cash to double.

Can I double my money in 5 years?

Absolutely, but you'd need the right interest rate!

Using the Rule of 72, divide 72 by 5. You'll get 14.4%.

So, to double your money in 5 years, you'd need an investment with a yearly return of about 14.4%.

Not impossible, but you'll want to hunt for the right opportunity!

Does your money double every 7 years?

Money only doubles if it earns interest, and for 7 years specifically it also depends on the interest rate.

If you're getting a 10% return on your money, the Rule of 72 says you'll double it in about 7.2 years.

So yes, with a 10% interest rate, it's pretty close!

Remember, the higher the rate, the quicker the double.

How long to double money at 8 percent?

Dividing 72 by 8 gets 9.

That means with an 8% interest rate, your money would take roughly 9 years to double.

It's a nice way to see how your investment can grow over time!


The Rule of 72 is an easy way to guess how long it takes for your money to double with a certain interest rate.

Just divide 72 by the interest rate to get the years. It works best for interest rates between 4% and 20%.

For really low rates, like 1% to 3%, the "Rule of 70" is better.

This rule helps whether you're saving for a kid's future or your own retirement.

But remember, it's just a rough guide, not an exact answer.

Join a Community of Great Gifters!

Easy & Meaningful Gifting Experience

I love how easy it is to give a meaningful gift to the kids and tots in my life!
It means a lot to me that I can contribute to their future, and Greatest Gift makes the experience seamless and fun.

Alana S.

Best Birthday

Our son just turned two. We created his gifting page with Greatest Gift and shared it on the birthday evite. The results were amazing! We received 12 gifts that will be going to his college fund and savings.
Love this platform.

Daniel A.

Love The Discover Section

We have a 2-year-old and another baby on the way, and we love Greatest Gift’s discover section. I look forward to learning about the right financial tools to help build their future and set them up for success financially.

Hillan K.

As Featured In

A Guide for your Financial Parenting Journey

Discover guides and compare financial products that
set your kids up for a great financial future