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Rule of 72


The Rule of 72 is a simple financial formula used to estimate the number of years it would take to double an investment or debt with a fixed annual rate of interest, without considering additional contributions. You divide 72 by the annual interest rate, and the result is approximately the number of years required. This rule provides a quick and easy approximation for calculations of compounding interest.


The phonetic pronunciation of “Rule of 72” would be: rool ov sev-en-tee-too.

Key Takeaways

<html><body><ol><li>The Rule of 72 is a simple formula used in finance that helps to estimate the number of years required to double the invested money at a given annual rate of interest.</li><li>The rule states that you divide the rate, expressed as a percentage, into 72. For example, if you want to know how long it will take to double your money at eight percent interest, you divide 8 into 72 and get 9 years.</li><li>While it provides a good estimate, the Rule of 72 isn’t exact, especially with larger rates of interest. It is, nevertheless, a simple and useful rule of thumb for evaluating investment opportunities.</li></ol></body></html>


The Rule of 72 is a significant term in business and finance as it provides an efficient method to estimate the amount of time required to double an investment given a fixed annual rate of interest. By dividing 72 by the interest rate, investors can quickly calculate approximately how many years it will take for the initial investment to duplicate itself. This rule, although a simple mathematical approximation, is a powerful tool, aiding in the swift comparison of the potential effectiveness of different investment opportunities. It gives investors intuitive financial foresight, allowing for better planning and decision-making, thus playing a crucial role in financial management and investment strategy.


The Rule of 72 is a quick, simple method used in finance to determine the amount of time it would take for an investment to double, given a fixed annual rate of interest. This rule allows investors and financial experts to make swift estimations and decisions on their investments without complex calculations. By simply dividing 72 by the annual rate of return, investors can get a rough estimate of how many years it will take for the initial investment to duplicate itself.The main purpose of the Rule of 72 is to provide a guideline or tool for investors and financiers to estimate the time or interest rate needed to double a potential investment. This rule is incredibly helpful in approximation of compound interests in various financial situations such as investments, inflation rates, and personal savings. A practical example could be that with an annual interest rate of 6%, an initial investment would roughly double in value in 12 years (i.e., 72/6) as per the Rule of 72.


The Rule of 72 is a simple way to determine how long an investment will take to double given a fixed annual rate of interest. Here are three real-world examples:1. Retirement Savings: Suppose you have $50,000 in your retirement account that earns 6% interest per year. Using the Rule of 72, you can estimate that your money will double in about 12 years (72 ÷ 6 = 12). This estimation can help in long-term retirement planning.2. Loan Interest: If you took out a loan at a 9% interest rate, you could use the Rule of 72 to figure out how long it would take for the loan amount to double if you made no payments. In this case, it would take about 8 years for the loan balance to double (72 ÷ 9 = 8).3. Saving Account: Let’s say you have a savings account with $10,000 and the bank offers you a 3% interest rate. If you want to know how long it will take for your savings to reach $20,000 at this rate, the Rule of 72 tells you that it will take approximately 24 years (72 ÷ 3 = 24).Please remember these are just estimations and actual results might have minor variations due to compounding periods or changes in interest rates.

Frequently Asked Questions(FAQ)

What is the Rule of 72?

The Rule of 72 is a simplified formula in finance that helps to estimate the number of years required to double the money at a fixed annual interest rate.

How does the Rule of 72 work?

You can apply the Rule of 72 by dividing the number 72 by the rate of return. For instance, for a 6% rate of return you get 12 years (72/6).

Is the Rule of 72 accurate?

It is a close approximation and serves as a general guideline. The actual figure may be slightly off due to variations in interest compounding.

Can the Rule of 72 be used for decreasing value like inflation or loan interest?

Yes, you can use the Rule of 72 to find out how long it would take for money’s value to halve due to inflation or to figure out when a loan balance would decrease to half with constant repayments.

Does compounding frequency affect the Rule of 72?

Yes, more frequent interest compounding will make the money double more quickly than the Rule of 72 predicts.

Can the Rule of 72 account for additional regular investments?

No, the Rule of 72 is only applicable when considering a lump sum investment without additional regular contributions.

How is the Rule of 72 used in the business world?

It’s often used by investors, financial planners, and advisors as a quick and easy calculation to estimate the timeline for returns on an investment.

What is the mathematical basis for the Rule of 72?

The Rule of 72 is derived from the formula for exponential growth. It’s a close approximation of the true mathematical formula that’s easy to calculate in your head or on a basic calculator.

Related Finance Terms

  • Compound Interest
  • Inflation Rate
  • Investment Duration
  • Annual Interest Rate
  • Financial Forecasting

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