Form 8606 - Partial Roth Conversion from IRA with basis

[rusty1992]

Form  8606 Part 1 Line asks for total Traditional IRA value (as 12/31 previous year) , to calculate the percentage factor to determine how much of the conversion is pre-taxed contribution vs untaxed contribution.   

Most external advice I can find is that I should enter in Line 6 the  total value of "the" traditional IRA  that I am doing a partial Roth conversion from. (which I would prefer to do)  However the IRA guidance states to enter the value of "all" IRAs (If I'm reading it correctly) and not just the traditional IRA where there is basis and I am converting.   None of my other IRAs have any (already taxed contributions) basis in them. 

Which figure for 'total IRA value should I use? the total of the affected IRA (the one I'm converting from, or my total IRA portfolio (other companies)? 

It makes a huge this-year tax difference, and if I am using the larger number, I'll be doing this % percentage calculation for many years to come.  I rather move this IRA in two years, and take credit for approx. 50% of the basis each of the two filing years, and be done with it.  I would assume the bigger no-no is claiming more basis that I actually have, which I'm not. 

[dmertz]

The year-end value to enter is the total amount that you had in traditional IRAs (which includes rollover, SEP and SIMPLE IRAs) of which you are the participant.  Do not include any Roth IRAs, any non-IRA accounts line 401(k)s, any IRAs maintained for your benefit as beneficiary or anyone else's IRAs.

Your basis in nondeductible traditional IRA contributions belongs to you, not to any particular one of your traditional IRAs.  For the purpose of From 8606, all of your traditional IRAs are treated in aggregate as one large IRA.