When to retire and how much money you need to do so is a hard question for many people. The website investopedia says you should assume you will need 80 percent of your annual salary to maintain your standard of living. To find out if you will have enough, you start by adding up your savings and investments and figure out what kind of yearly return you can expect. Six to ten percent is about right. If you have a pension plan, obtain an estimate of that value and then do the same with social security. If it doesn't add up it may be time to set aside more money.