401(k) In-Plan Roth Conversion - how to report the "income" in taxes?

[RetireAbroadAt35]

I'm trying to complete my 2023 taxes, which have changed quite a bit since I FIREd.  I'm filing as single, with my only income being from dividends and the taxable impact of my 401(k) in-plan Roth conversion.  I also have a traditional and a roth IRA that I have not contributed to during 2023.

I'm filling out PDF forms using a spreadsheet for calculations.  I've been doing my taxes manually for years but right now I'm struggling with reporting my 401(k) In-Plan Roth conversions. 

I have a 1099r with Vanguard that shows the $20k I converted.  I think this gets reported on form 8606, lines 16-18.  The instructions all reference IRAs so I'm not sure I'm on the right page.

• Is this handled through form 8606?  With the result going on my 1040 line 4?  Double-checking since the forms all talk about IRAs and this is a 401(k) in-plan conversion.
• If so, am I correct that the amount in 1099r box 1 and 2a (both have the same value) goes in 8606 lines 16 and 18?
• It's not clear to me if I need to complete Part 1 of the 8606 as well.
• And finally, I don't understand the instructions in regards to line 17 (basis).  Logically it seems that if the entire $20k is taxable that line 17 should be 0.

I think that in the end I'm trying to put $20k in my 1040 line 4a and 4b but I'm not sure how to get there.

[MDM]

Don't read into the Form 8606 instructions anything that isn't there.  E.g., Part II is for "2023 Conversions From Traditional, Traditional SEP, or Traditional SIMPLE IRAs to Roth, Roth SEP, or
Roth SIMPLE IRAs".  It says nothing about a 401k.

See the Form 1040 Instructions for Lines 5a and 5b.

[RetireAbroadAt35]

I know it doesn't talk about 401ks - hence my question.

Anyhow, thank you.  I've been been using 8606 for my IRA contributions for so long I had some tunnel vision going on. 

If I understand the instructions correctly, this is pretty simple, and all I need to do is put the $20k from 1099r box 2a (taxable amount) into line 5b and call it a day.

[MDM]

I know it doesn't talk about 401ks - hence my question.

Anyhow, thank you.  I've been been using 8606 for my IRA contributions for so long I had some tunnel vision going on. 

If I understand the instructions correctly, this is pretty simple, and all I need to do is put the $20k from 1099r box 2a (taxable amount) into line 5b and call it a day.

Yes, you understand correctly.  No 8606 needed for this, and that's all that's needed on form 1040.  Well done!

[RetireAbroadAt35]

Muchas gracias!  This has been an interesting transition - life, taxes, etc.  I went from managing my finances with spreadsheets on a weekly/monthly basis to being completely averse to looking at anything other than necessary monthly bills.

And I will admit I put off doing my 2022 so I am trying to get caught up on everything. 

I think this is the last piece of the puzzle.

My goal this year will be to figure out how to optimize my allocations and taxes during my no income years.  Clearing this backlog will go a long way to making that possible.

[terran]

The $20k taxable amount should go on line 5b and the word ROLLOVER should also be written to the left of the box to indicate this was not distribution.