Assuming long-term market returns stay more or less the same, the Rule of 72 tells us that you should be able to double your money every 7.2 years. So, after 7.2 years have passed, you'll have $200,000; after 14.4 years, $400,000; after 21.6 years, $800,000; and after 28.8 years, $1.6 million.