Given the choice, should one switch from Roth to traditional IRA/401k contributions as one approaches retirement, and if so is there any good way to decide when?
If it affects the decision, I am hoping that my investments, combining both flavors of 401k and taxed investments, will let me spend $70k of income per year, so depending on where that's drawn from my tax rate is sorta tangled into this question... but initially I suspect it won't drop a lot.
My simplest approach is to suggest that people go Roth when in the 15% bracket, and use pre-tax to avoid 25%. I outlined that strategy in my article The 15% solution.
The monkey wrench that gets thrown in to this is the distortion of the other smooth marginal tax curve caused by the taxation of social security. For those who can afford to, it makes the case to lean toward Roth as much as possible.
I'd suggest always depositing pretax, and using conversions to better control the process. Two major benefits to this.
It's less a question of too late than of what strategy to use.
Years before retirement isn't related at all to the Pretax IRA/Roth IRA decision, except insomuch as income typically trends up over time for most people. If tax rates were constant (both at income levels and over time!), Roth and Pretax would be identical. Say you designate 100k for contribution, 20% tax rate. 80k contributed in Roth vs. 100k contributed in Pretax, then 20% tax rate on withdrawal, ends up with the same amount in your bank account after withdrawal - you're just moving the 20% tax grab from one time to another.
If you choose Roth, it's either because you like some of the flexibility (like taking out contributions after 5 years), or because you are currently paying a lower marginal rate than you expect you will be in the future - either because you aren't making all that much this year, or because you are expecting rates to rise due to political changes in our society.
Best is likely a diversified approach - some of your money pretax, some posttax. At least some should be in a pretax IRA, because you get some tax-free money each year thanks to the personal exemption. If you're working off of 100% post-tax, you are paying more tax than you ought unless you're getting enough Social Security to cover the whole 0% bucket (and probably the 10% bucket, also).
So for example, you're thinking you want 70k a year. Assuming single and ignoring social security (as it's a very complicated issue - Joe Taxpayer has a nice blog article regarding it that he links to in his answer), you get $10k or so tax-free, then another $9k or so at 10% - almost certainly lower than what you pay now. So you could aim to get $19k out of your pre-tax IRA, then, and 51k out of your post-tax IRA, meaning you only pay $900 in taxes on your income.
Of course, if you're in the 25% bucket now, you may want to use more pretax, since you could then take that out - all the way to around $50k (standard exemption + $40k or so point where 25% hits). But on the other hand, Social Security would probably change that equation back to using primarily Roth if you're getting a decent Social Security check.
