What is the Rule of 72 in money?

The Rule of 72 is a simple, time-tested formula used in finance to estimate how long it will take for an investment to double in value, given a fixed annual rate of return. The rule is often applied by investors, financial planners, and individuals who want to understand the power of compound interest and make more informed financial decisions.
This tells you that it will take about 12 years for your investment to double in value at a 6% interest rate.
Practical Uses of the Rule of 72
The Rule of 72 is primarily used to estimate the effect of compound interest, helping you evaluate investment options or compare savings strategies. Here are some common applications:
- Investments: Whether in stocks, bonds, or mutual funds, the Rule of 72 helps investors gauge how long it will take for their capital to grow.
- Interest Rates on Loans: The rule also applies to debt. If you know the interest rate on a loan or credit card, the Rule of 72 can give you an idea of how fast your debt could double if unpaid.
- Inflation: If inflation averages 3%, the Rule of 72 shows that it would take roughly 24 years for the purchasing power of money to halve.
- Retirement Planning: It provides an easy way to visualize how different rates of return will affect your retirement savings.
Limitations of the Rule of 72
While the Rule of 72 is a handy shortcut, it does have its limitations:
- The formula works best for interest rates between 6% and 10%. For very high or low rates, the approximation becomes less accurate.
- It assumes a consistent rate of return, which isn’t realistic in volatile markets.
Importance of Compound Interest
The Rule of 72 underscores the importance of compound interest, which is the interest on both the initial investment and the interest that has been added to it over time. Understanding compound interest can help you recognize the value of saving early and allowing your money to grow over time.