What do you make of this question? If my portfolio amount will allow for a withdrawal rate of, say $30,000 per year and achieve 99% FIREcalc results, what happens if in, say, 5 years the portfolio increases to a level where FIREcalc says I can withdraw $50,00 per year and still achieve 99%? Can you reset the annual withdrawal amount based on better than expected returns? This would seem to fly in the face of the underlying principle. Same question holds for any calculation of withdrawal amounts - like the 4% rule.