Assuming you average 7% each year on the S&P 500, inflation averages 3%, and 50K per year is your target, you would want at least 1.25 million USD in the bank.

Assuming you average 7% each year on the S&P 500, inflation averages 3%, and 50K per year is your target, you would want at least 1.25 million USD in the bank. Taking into account volatility, you'd probably want at least 1.8M.