Yes the $6,000 non-deductible basis, if that is the only money in all Traditional IRA accounts that exist at the end of 2021 (Dec 31, 2021), will offset the tax on the 2021 conversion. You can also make a 2021 non-deductible $6,000 contribution and convert the entire $12,000. That will go on your 2021 tax return in when you file in 2022.
(If you were thinking that this could be reported on your 2020 tax return then sorry, any 2020 conversion must have been completed by Dec 31, 2020. If after that and in 2021 then it is reported on your 2021 tax return.)
The 2020 non-deducible contribution IS reported on your 2020 tax return on a 8606 form which you will need when you do your 2021 tax return for the conversion.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
