I am not asking about a conversion from 401K to Roth IRA. (That'd be Form 8606 by the way).

My employer plan allows both traditional and Roth 401(K). Really. They also allow Roth conversions from traditional 401(K) to Roth 401(K).

However, the Roth conversion needs to be reported on taxes. What form is used?

By all evidence, Form 8606 is the wrong form for conversions to Roth 401(K) since neither the form nor the instruction contains the keyword "401" anywhere in it. Am I mistaken about that?

(There was a joke in M.A.S.H. where a field platoon could get a soda fountain, they just took a different military form and crossed out "Machine gun" and wrote "Soda fountain". Is this like that, and I use 8606 anyway? Do I cross something out?). I also have IRAs and I don't want those confused.

1 Answer 1


You do not report roll over from 401k to Roth IRA on form 8606, only from Traditional IRA.

You will get a 1099-R from your 401k plan showing the total converted amount (as distributed from the pre-tax 401k under a roll-over code) and the taxable portion of that.

The total amount should show up on your form 1040 line 5a and the taxable portion of that should show up on your form 1040 line 5b.

No other reporting is necessary as the plan is responsible for tracking your after tax basis (as opposed to the IRA where you need to do that yourself using form 8606).

  • 1
    Well, that's convenient....
    – keshlam
    Apr 17, 2023 at 23:52
  • IRA conversions also use 1099-R. But 8606 is needed to fill in the missing after-tax basis.
    – Ben Voigt
    Apr 18, 2023 at 16:57

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