The Rule of 72 Where are some places we keep our money when we're not spending it? Piggy banks, the back of your smelliest drawer, in your mattresses? How about banks, mutual funds, stocks, bonds or bonds? So what's the difference between keeping your money in your mattresses and keeping it in the bank? Well, a $10.00 deposit will grow to $10.52 in one year if it earns 5% interest annually, compounded monthly. After three years you would have $11.62. That same $10.00 kept in a piggy bank at home would still be only $10.00 after three years. Do You Know the Rule of 72? Saving money is a great way to grow your money! Banks pay you for keeping your money in a savings account. The bank pays "interest" which is expressed as a "percentage rate." So, the more money you keep in a savings account, the more interest you will earn. Money kept in a savings account will eventually double. If you divide 72 by the rate of interest, you will discover how many years it takes to double your money!