The Rule of 72 is a quick way to estimate how long it will take for an investment to double in value, given a fixed annual interest rate. It works by dividing 72 by the interest rate. For example, an investment at 8% interest will roughly double in 9 years (72 / 8 = 9) according to AmeriServ.
1. Find the interest rate:
Determine the annual interest rate of your investment (e.g., 6%, 10%, etc.).
2. Divide 72 by the interest rate:
Divide 72 by the interest rate to get an approximation of how many years it will take for your investment to double.
- For example, if your interest rate is 4%, it will take approximately 18 years for your investment to double (72 / 4 = 18).
- If your interest rate is 9%, it will take approximately 8 years (72 / 9 = 8).
Important Considerations:
- Approximation: The Rule of 72 is an approximation, not an exact calculation. The accuracy decreases as the interest rate deviates significantly from 8%.
- Compounding: The rule assumes compound interest, where interest earned is added to the principal, and then the next interest calculation includes the original principal plus the accumulated interest.
-
Inflation: Inflation can erode the purchasing power of your investment over time. The Rule of 72 can also be used to estimate how long it takes for the value of money to be halved due to inflation, according to Saxo Bank.
-
Other Factors: The Rule of 72 doesn’t account for taxes, fees, or changes in interest rates.
