If you follow any of the FIRE (financial independence / retire early) posts or blogs, a simple place to start is to take your current annual household expenses and multiply by 25. Using that number, if you stick to a 4% withdraw annually you will never run out of money. Example - if you spend $80,000 last year (house, groceries, car, etc...) multiply by 25. 80,000 X 25 = $2,000,000. You will never run out of money if you stick to a 4% withdrawal annually. LOTS of caveats and assumptions but it gives a GENERIC starting point that's close to being in the ball-park. Your results WILL vary. Personally I've used numerous on-line models and have a financial planner because I don't want to get this one wrong.