How Long to Double Money at 4% – Rule of 72
At a 4% annual return, your money doubles in approximately 18 years according to the Rule of 72.
How to use this tool
- Enter annual rate in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your years to double and the full breakdown beneath it.
Use the Rule of 72 to see how a 4% annual interest rate doubles your money in about 18 years.