I've considered this issue before. How much is 'enough'? It certainly depends on what your preference is (are you okay with second hand cars, or do you want to try a Lamborghini for size?), but $5M in the bank is 50 years at $100K a year (ignoring interest, etc). Towards the end of your life you probably don't need that much, but if you didn't want to have 'too much' and were disciplined enough to leave most of what you have in the bank and just give yourself an 'allowance', $5M would not be an unreasonable sum.