I think it is important to consider investment return in addition to marginal tax rates before and after retirement. Suppose that I invested $1,000 in a Roth when I was 20, and it grows to $32,000 before I take it out 50 years later (average return around 7%). Suppose that my initial tax rate was 40% and my ending tax rate is also 40%. Even though my marginal rate hasn't changed, I am better off with the Roth. I paid taxes of $400 in the beginning, and I pay no more when I withdraw. Now compare that to a traditional IRA. I set aside my initial $400 tax savings into an account that gets exactly the same return as my IRA, and I have the discipline not to touch it. At the end, it is worth $12,8000, which equals the taxes due on my withdrawal from a taxable IRA, so it seems like a wash -- but it is not, because I will now also have to pay capital gains taxes on $12,400 of the money I set aside to pay for the taxes. Today, that would be 20% for a total extra tax of $2,480. My post-retirement tax rate would need to be substantially lower than my pre-retirement rate to break even in this scenario, because of the large amount of gains.