I have a traditional IRA, which has money which has been contributed three different ways:

  1. deductible IRA contributions
  2. non-deductible IRA contributions
  3. rollover from 401(k)

I'm looking at converting this to a Roth IRA in 2010, now that there's no income limitation. I also may only convert part of my traditional IRA this year, to avoid a bump in the marginal tax rate.

I also have a Roth 401(k), although I don't think this has any effect.

How would the calculations work for how much tax I would owe? Are there any other things I should be aware of?

  • OK, so you have a Traditional IRA, a Roth IRA, and a 401(k). Which are you wanting to move funds out of, and which are you wanting to move funds into? Oct 22, 2010 at 22:56
  • @Benjamin Chambers Converting from the Traditional IRA to a Roth IRA. As far as I know, there's no other type of allowable conversion.
    – DanTilkin
    Oct 23, 2010 at 4:20

2 Answers 2


Conversions are done on a pro-rata basis. If you haven't yet paid tax on the money, you need to do so in the process of converting.

Let's say you have a total of $50k in your account:

  • $10k in deductible contributions
  • $10k in non-deductible contributions
  • $20k in 401(k) rollover funds
  • $10k in as-yet untaxed earnings

If you decide to convert half of this to a Roth ($25k), you'd owe tax on $20k of that, because 80% of your holdings in the traditional IRA have not been taxed yet. The non-deductible contributions have been taxed, so you don't need to pay tax again on that part.

More information is here.


MB's math is right, but I can describe it in a short sentence. All Traditional accounts are combined, 401(k) rollover is no different from other IRA money. You should have been tracking your non-deducted money via form 8606 so you know this figure. The non-deducted money as a percent of your total balance is the percent of conversion that's not taxed. (To be clear, deducted contributions and growth are not tracked separately, one only tracks the non-deducted deposits.)

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