Sounds like you are trying to add all of your expected expenses together to come up with an amount you'll need to retire. You will pay taxes on your 401(k) withdrawals which are considered ordinary income so this needs to be considered. However, I would recommend first deciding how old you plan to be when you retire and how long you will need the money to last. Of course, you can't know this but you have to make some projections. Also, many financial advisers say you can only take up to 5% or so out of your retirement accounts each year to live on if you want the money to keep growing sufficiently. The Financial Planning Association is now touting research that shows you need more money in your first retirement years than your later retirement years. Have you considered that?

Unless you have tackled these issues, I don't think trying to come up with a specific amount of money you'll need will work.

There is a free 40-year MS Excel investment calculator at the URL below. It allows you to put in your age, current investment level, principal additions, ROI, and an inflation rate to get the best possible estimate on what your long-term investment goal should be.

It won't help you calculate taxes, but it can help you answer the other side of your equation.

Good luck,

There is no correct answer to this question. It depends on your assumptions. Look at what your effective tax rate right now. It is probably not 24% you may be in a 25% tax bracjet but the effective tax rate is less. The effective tax rate is
(Total Tax) / (Adjusted Gross Income), probably no more than about 10-15%.
At retirement you will not be paying social security tax, but you will be paying federal and state income taxes on withdrawals. Now what I suggest is check with your employer if they offer ROTH 401k, and maybe split your contributions between the two (ROTH and Regular 401k). When you retire, this may help avoid taxes altogether.
Say you need 100K per year at retirement, if you withdraw the whole thing from 401K, you will pay whatever tax rate is at that time. Now if you withhold 50K from ROTH account and 50K from regular 401K, then you only pay tax on 50K, since tax rates are gradual, at that time 50K may not even be enough to pay any tax, this why in presence of ROTH account, a regular one becomes in fact non-taxable either.