# What is the Rule of 72 in Finance?

In the world of finance, there are concepts that make complex financial calculations simpler and show us easier and smarter ways to handle money. One of these is the ‘Rule of 72.’ This clever formula changes how we think about investing.

In this article, we’ll dig into what the Rule of 72 really means. We’ll explain and unravel its simple and powerful methodology to estimate your investment growth. Whether you’re new to finance or are an expert in finance, let’s learn more about how this rule works, where we can use it, and why it’s super important in the business world.

## What is the Rule of 72?

The Rule of 72 is a fundamental financial concept that provides a quick and easy way to estimate the time it takes for an investment to double in value, based on a fixed annual rate of return. This rule offers a simplified approach to understanding the power of compounding interest and its impact on the growth of investments.

In essence, the Rule of 72 allows you to determine approximately how long it will take for your initial investment to become twice its original value, given a certain rate of return. This concept is particularly useful for making rough calculations and setting general expectations about the growth potential of different investments.

## The Rule of 72 formula

See the formula for the Rule of 72 above and below:

Years to Double = 72 / Annual Rate of Return

In this formula:

• Years to double: This is the number of years it takes for an investment to double in value.
• 72: This is a constant number used in the formula.
• Annual rate of return: This is the expected annual percentage rate of return on the investment.

To use the formula, you simply divide 72 by the annual rate of return (as a percentage). The result will give you an approximate estimate of the number of years it will take for your investment to double in value based on the given rate of return. Keep in mind that this is a simplified calculation and is most accurate for interest rates between 6% and 10%. For rates outside of this range, the approximation may become less precise.

## Practical examples of using the Rule of 72

To better understand how to apply the Rule of 72, let’s go through some examples:

1. Investment with 6% annual interest
Using the formula “Years to Double = 72 / 6,” we find that it will take approximately 12 years for this investment to double in value.
2. Investment with 9% annual return
Using “Years to Double = 72 / 9,” the result shows that 8 years are needed for the investment to double.
3. Savings account with 3% interest
Using “Years to Double = 72 / 3,” we find that it will take about 24 years for the money in a savings account with a 3% interest rate to double.

These examples demonstrate how the Rule of 72 can be used to quickly gauge the time needed for an investment to double, given various rates of return.

## Is the Rule of 72 accurate?

It’s important to note that the Rule of 72 is an approximation and has limitations. Its accuracy can vary depending on the interest rate being used and the specific circumstances of the investment.

The Rule of 72 is most accurate for interest rates within the range of 6% to 10%. Within this range, the approximation is generally quite close to the actual time it takes for an investment to double. However, as the interest rate moves away from this range, the accuracy of the rule diminishes. For interest rates significantly lower than 6% or higher than 10%, the Rule of 72 becomes less precise.

Additionally, the Rule of 72 assumes that the interest is compounded annually, which may not always be the case with all types of investments or financial instruments.

Despite its limitations, the Rule of 72 remains a valuable tool because of its simplicity and quick mental calculation. It provides a rough estimate that can help individuals quickly gauge the potential growth of their investments and make informed financial decisions. For more accurate calculations, especially with interest rates outside the 6% to 10% range, using more complex financial tools and formulas would be recommended.

## How to use the Rule of 72

Using the Rule of 72 is straightforward and involves a simple calculation. Follow these steps to apply the Rule of 72 to estimate how long it will take for an investment to double in value:

1. Determine the investment rate of return: Begin by identifying the annual rate of return for the investment. This rate should be expressed as a percentage. It represents the expected growth rate of the investment per year.
2. Use the Rule of 72 formula: Use the previously determined formula. Divide 72 by the annual rate of return (as a percentage) to calculate the approximate number of years it will take for the investment to double.
3. Interpret results: The result of the calculation represents an estimation of the number of years it will take for your investment to double in value based on the given annual rate of return.
4. Consider any limitations: Be aware of the limitations of the Rule of 72. For rates outside of the 6-10% range, the accuracy decreases. Additionally, the rule assumes annual compounding, which might not apply to all investment types.
5. Only use as a guideline: Remember that the Rule of 72 provides a quick estimate, not an exact calculation. It’s a useful tool for getting a rough idea of how long it might take for an investment to double, but it might not be precise enough for detailed financial planning.
6. Ensure multiple scenario analysis: You can use the Rule of 72 for different types of investments. However, keep in mind that the rule’s accuracy can vary based on the type of investment and its specific characteristics.

In summary, the Rule of 72 is a quick and simple way to estimate the time it takes for an investment to double based on a fixed annual rate of return. It’s a handy tool for making rough calculations and setting general expectations about investment growth.

## When do you need the Rule of 72?

The Rule of 72 is a useful tool in various financial situations where you need a quick estimate of how long it will take for an investment to double in value. Here are some scenarios where the Rule of 72 can be particularly handy:

1. Planning for investments: When considering different investment opportunities, the Rule of 72 can help you quickly compare the growth potential of investments with varying annual rates of return. It allows you to get a general sense of how long it might take for your investments to double and make initial assessments.
2. Planning for savings: If you’re setting savings goals for the future, the Rule of 72 can assist you in estimating the time required to reach your desired savings amount. This can be especially helpful for long-term financial planning.
3. Planning for retirement: When planning for retirement, you can use the Rule of 72 to understand how your retirement savings might grow over time based on different investment returns. This can help you gauge if you’re on track to meet your retirement goals.
4. Planning for education: Parents and students can use the Rule of 72 to estimate how long it might take for an education fund to double. This can aid in setting aside funds for education expenses with a rough idea of their potential growth.
5. Managing your debt: The Rule of 72 can be applied to estimate the time it might take for a debt to double if left unpaid. This can highlight the importance of managing debt and making timely payments.
6. Comparing investment options: When comparing different investment options, the Rule of 72 can provide a quick gauge of which investment might offer faster growth potential based on their respective rates of return.

### Limitations of the Rule of 72

While the Rule of 72 is a useful tool for estimating investment growth, it has several limitations that should be considered:

• Limited accuracy: As discussed, the Rule of 72 becomes less accurate as the interest rate deviates from the 6% to 10% range. For interest rates significantly lower or higher than this range, the estimation becomes less reliable.
• No account for inflation: The Rule of 72 doesn’t take into account the effects of inflation, which can significantly impact the purchasing power of your investment returns over time.
• Simple interest vs. compound interest: The rule assumes that the investment’s interest is compounded, meaning that the interest is added to the principal amount, and future interest is calculated based on the new total. If the investment earns simple interest, where interest is calculated only on the initial principal, the Rule of 72 will not apply accurately.
• Doesn’t account for tax implications: The rule doesn’t consider the tax implications of investment growth. Taxes on interest, dividends, or capital gains can affect the actual growth of an investment.
• Ignores external factors: The Rule of 72 doesn’t account for external factors that might impact investment growth, such as economic fluctuations, market volatility, or changes in the investment’s value.
• Limited to doubling: The Rule of 72 is specifically designed to estimate the time it takes for an investment to double. It doesn’t provide information about other growth scenarios, such as tripling or quadrupling.
• Not suitable for short-term investments: The rule is best suited for estimating growth over the long term. For short-term investments or those with very low rates of return, the rule may not be as applicable.
• Assumes a constant rate: The Rule of 72 assumes a constant rate of return. In reality, rates of return can fluctuate, affecting the actual growth trajectory of the investment.

Despite these limitations, the Rule of 72 remains a valuable tool for making quick estimations and getting a general sense of how investments might grow over time. However, for more accurate and detailed calculations, especially in complex financial scenarios, it’s advisable to use more advanced financial tools and formulas.

## Track the Rule of 72 in a financial planning tool

A financial modeling tool like Brixx can certainly help track the Rule of 72. Financial modeling tools are designed to perform complex calculations, analyze data, and provide insights into various financial scenarios. When it comes to the Rule of 72, a financial modeling tool can assist by automating calculations and visualizing how investments might grow over time based on this rule.

Here’s how a financial modeling tool could help with tracking the Rule of 72:

• Automated calculations: Brixx can automate the Rule of 72 calculation for different scenarios. You input the initial investment, the annual rate of return, and the tool can quickly compute and display the estimated time it takes for the investment to double.
• Scenario analysis: Brixx allows you to create multiple scenarios with different investment parameters. You can compare how changes in the rate of return affect the doubling time and investment growth.
• Visualization of data: Brixx offers visualization features like charts and graphs. You can use these visuals to see how the investment grows over time and where the doubling point occurs.
• Sensitivity analysis: You can assess how variations in interest rates impact the estimated doubling time, giving you insights into the sensitivity of the result.
• Educational tool: Financial modeling tools can serve as educational tools by demonstrating the effects of compounding interest and helping users understand the Rule of 72.

Ready to take control of your investments? Take some time to explore the features of our financial planning software. Determine how it can benefit you and your business in calculating how long it will take for your investments to double.