The Rule of 72 (2024)

FAQs

What is the Rule of 72 answer? ›

Just take the number 72 and divide it by the interest rate you hope to earn. That number gives you the approximate number of years it will take for your investment to double.

The Rule of 72 is reasonably accurate for low rates of return. The chart below compares the numbers given by the Rule of 72 and the actual number of years it takes an investment to double. Notice that although it gives an estimate, the Rule of 72 is less precise as rates of return increase.

The Rule of 72 is a calculation that estimates the number of years it takes to double your money at a specified rate of return. If, for example, your account earns 4 percent, divide 72 by 4 to get the number of years it will take for your money to double. In this case, 18 years.

Advantages and Disadvantages of Rule of 72

However, the Rule of 72 is based on a few assumptions that may not always be accurate, such as a constant rate of return and compounding period. It also does not take into account taxes, inflation, and other factors that may impact investment returns.

Key Takeaways

The Rule of 72 is a simplified formula that calculates how long it'll take for an investment to double in value, based on its rate of return. The Rule of 72 applies to compounded interest rates and is reasonably accurate for interest rates that fall in the range of 6% and 10%.

The Rule of 72 is a convenient method to estimate the approximate time for invested capital to double in value. By merely taking the number 72 and dividing it by the rate of return (or interest rate) expected to be earned, the output is the approximate number of years for an investment to double.

The accuracy of the rule of 72

The rule of 72 gives 72/9 = 8 years, which is close to the exact answer.” However, Stanford adds that the rule of 72 is only an approximation that is accurate in a range of interest rates between 6% and 10%. Outside that range, the error can vary as little as 2.4% to as much as 14%.

One of the easiest ways to double $1,000 is to invest it in a 401(k) and get the employer match. For example, if your employer matches your contributions dollar for dollar, you'll get a $1,000 match on your $1,000 contribution.

You can also apply the Rule of 72 to debt for a sobering look at the impact of carrying a credit card balance. Assume a credit card balance of $10,000 at an interest rate of 17%. If you don't pay down the balance, the debt will double to $20,000 in approximately 4 years and 3 months.

Who invented the Rule of 72? ›

Albert Einstein often gets credit, but Italian mathematician Luca Pacioli most likely invented, or introduced the Rule of 72 to the popular world in the late 1400s.

The 20/10 rule of thumb is a budgeting technique that can be an effective way to keep your debt under control. It says your total debt shouldn't equal more than 20% of your annual income, and that your monthly debt payments shouldn't be more than 10% of your monthly income.

It is not an exact value and can only provide a general estimate of the time required to double the investment. If the interest rate changes due to some factor, the Rule of 72 becomes null and void. The Rule of 72 does not apply to changing interest rate investments or basic interest investments.

The Rule of 78 is an important consideration for borrowers who potentially intend to pay off their loans early. The Rule of 78 holds that the borrower must pay a greater portion of the interest rate in the earlier part of the loan cycle, which means the borrower will pay more than they would with a regular loan.

Basically, the rule says real estate investors should pay no more than 70% of a property's after-repair value (ARV) minus the cost of the repairs necessary to renovate the home. The ARV of a property is the amount a home could sell for after flippers renovate it.

The number of years it takes for a certain amount to double in value is equal to 72 divided by its annual rate of interest.

The Rule of 70 Formula

Hence, the doubling time is simply 70 divided by the constant annual growth rate. For instance, consider a quantity that grows consistently at 5% annually. According to the Rule of 70, it will take 14 years (70/5) for the quantity to double.

The Rule of 70 is a calculation that determines how many years it takes for an investment to double in value based on a constant rate of return. The Rule of 72 is a shortcut or rule of thumb used to estimate the number of years required to double your money at a given annual rate of return and vice versa.

You can also run it backwards: if you want to double your money in six years, just divide 6 into 72 to find that it will require an interest rate of about 12 percent.