Yes, definitely put in your best estimate of taxes other than RMDs, but RMDs vary year by year even if the market doesn't change and FireCalc can't see those changes in taxes. So a trick to get Firecalc closer is to reduce the balance of tax deferred you enter by the expected effective tax rate on RMDs. Then don't include taxes on RMDs in your tax estimates. Not perfect of course as if the total balance grows faster than inflation, then when you take RMDs the government's share is crowding out the lower brackets, making more SS taxable, etc.
Of course the big source of variability in the "Can I Retire Yet?" question is returns, not tax rates. FireCalc does a great job of illustrating how broad a typical range of outcomes could be and does so with just a small amount of input, so even people that hate playing with numbers will get a feel for where they are.
