If you’re not interested in doing the math in your head, this calculator will use the Rule of 72 to estimate how long a lump sum of money will take to double. Enter your data in they gray boxes. As a bonus, the Rule of 114 for tripling your money, and the Rule of 144 for quadrupling your money are included. For a more detailed compound interest calculator, with monthly investments, and daily, monthly, and annual compounding, please see The PoF Compound Interest Calculator.   Download all PoF calculators in one Excel file! You will be sent a link to the file and a confirmation to receive notifications of new posts and my quarterly progress note.