The sooner you start investing, the longer the period of time for compound interest to work, but make sure there isn't a better use for your money before investing. Some great uses for your money that you probably ought to consider before investing include paying off credit card debt, building an emergency fund large enough to keep you from going into debt due to typical financial emergencies, and getting the entire 401(k) match offered by your employer (not getting that is leaving part of your salary on the table.) Most investors do not wait until they are completely debt-free prior to investing, but if you have any debt other than a low-interest rate mortgage or low-interest rate student loans, realize that your best investment may be paying off your debt.