My husband had a traditional IRA with all pre-tax contributions. Learning of the backdoor Roth conversion, we contributed $8000 in 2025 as a nondeductible contribution and then converted that nondeductible amount to a Roth IRA. At the time, we were unaware of the pro-rata rule but learned of it just recently.
In order to be tax efficient, we want to roll the traditional IRA over to his employer sponsored 401(k) but I have read that we cannot roll over any basis that is in the traditional IRA. I have two questions about this:
1 - Since we have not had basis BEFORE this year, can we roll the entire amount of the traditional IRA (but not the amount in the Roth IRA) into the 401(k)?
2 - If the answer to 1 is no, then how do we calculate the basis left in the traditional IRA? For example, if the traditional IRA had 70K in it before the $8000 contribution, do we say 8k/78k = ~10.3% in basis so if we plan to roll over the pre-tax amount in the IRA we would roll over $62,790 which is 89.7% of the 70k? Or am I way off?
