I use both T.Rowe Price and FIRE calculators using the same set of data/info. I wanted a 99% confidence level. T. Rowe Price's calculator says that it is attainable with a 60/40 (Stock/Fixed income) portfolio but it is achievable with a 40/60 mix. FIRECalc, in contrary, indicates a higher rate of success as the equity portion of the portfolio increases. I think FIRECalc is more credible.