That depends entirely on the penny stocks you invest in, when you invest and when you exit. Therefore, it is important to do your research on the best penny stocks in Canada, checking their performance over 3-5 years before investing. If market conditions are in your favour, you may be able to double your investment capital within a year. But as with all investments, penny stocks too are prone to risks, and so there is no guarantee that penny stocks will give you the returns you are looking for.