The annualized return on the S&P 500 since its inception is 10 percent. Adjusted for inflation it's 6.5-7 percent. In the last 20 years, it's 5.9 percent. Adjusted for inflation it's 4.37 percent. So withdrawing 4 percent per year would be reasonable and keep up with inflation. It gets slightly more complex when you think about taking money out during down years is much larger impact than during good years, but that's an exercise for the reader.