Do a bottoms up estimate of what your monthly needs are. See if your income from a pension or SS will cover your basic need. If not, you will have to make that up somehow through part-time work or drawing off your 401K or IRAs/investments. Most common approach is to assume you take 4% a year from the nest egg, bump it by 3-4% a year to account for inflation, assume a 5-6% annual return (made up of 60% equities/ 40% bonds), and see how long it will last. Easy to build a excel spreadsheet to run out the numbers. Most people fall down in doing a good bottom up estimate. I tracked expenses for a year before convincing myself I could retire. Top level approach is assume you will need 70-80% of your current gross income. That always seemed high to me if you have no or little debt.