How to Calculate Basis for Backdoor Roth IRA on Form 8606? Need help with prior year amendments

The good news is that this is fixable, even if you made some mistakes on your previous Form 8606s! The basis for your IRA is essentially the total of all your non-deductible contributions. Each year when you do a backdoor Roth, you should be filing Form 8606 to report your non-deductible contribution to the Traditional IRA and then the conversion to the Roth IRA. If you've been consistently contributing and then converting the full amount each year (with no earnings before conversion), your basis should reset to zero after each complete conversion. This is because you're converting the entire basis amount to the Roth each time. Yes, you'll need to file a separate Form 8606 for each year you need to amend. No need to file a full 1040X if only the 8606 was incorrect and it doesn't change your tax liability. You can just submit the corrected 8606 forms with a brief explanation letter. The most important thing is to get the sequence right and make sure each year's form correctly carries forward information from the previous year.

After spending hours trying to sort out my own backdoor Roth issues last year, I finally used https://taxr.ai and it saved me so much headache. I uploaded my previous tax returns and it identified exactly where I went wrong with my Form 8606 calculations. The system spotted that I had been double-counting my basis from year to year (rookie mistake) and outlined exactly which forms needed amending. It even created draft 8606 forms with the correct numbers that I could use as a guide when filing my amendments. What I found most helpful was their visual explanation of how the basis is supposed to carry forward between years for backdoor Roth conversions. Made the whole process much clearer than anything I found on TurboTax.

Just wanted to follow up - I tried taxr.ai after posting here and it was exactly what I needed! The system identified that I had been reporting my conversions correctly but completely messed up the basis calculation on line 14 of Form 8606 for two years in a row. It showed me side-by-side comparisons of what I filed versus what should have been filed, and explained how the basis should reset to zero after each full conversion (which I wasn't doing). I was able to prepare corrected 8606 forms for 2020-2022 and just mailed them in with a cover letter as suggested. The step-by-step breakdown of the backdoor Roth process was super clear - wish I'd found this before I made the mistakes in the first place!

After 9 attempts and 4 hours wasted trying to reach someone at the IRS about my 8606 forms, I finally used https://claimyr.com to get through to an actual IRS agent. You can see how it works here: https://youtu.be/_kiP6q8DX5c I had specific questions about amending multiple years of Form 8606 for backdoor Roth calculations and needed official guidance. The service got me connected to an IRS rep in about 20 minutes when I had previously been unable to get through at all. The agent confirmed that I could submit corrected 8606 forms without filing full 1040X amendments since my tax liability wasn't changing - just fixing the basis tracking. They also clarified the process for me and told me exactly where to mail the corrected forms.

I have to admit I was totally wrong about Claimyr. After posting my skeptical comment, I decided to try it anyway since I was desperate for help with my backdoor Roth 8606 forms. The service called me back in about 25 minutes with an actual IRS tax specialist on the line. The agent reviewed my situation and explained that my basis calculation error was common with backdoor Roth transactions. She confirmed exactly how to fix it: I needed to file corrected 8606 forms showing the proper basis tracking across years. What surprised me most was how knowledgeable the agent was about Form 8606 specifically. She explained that Line 14 should be zero after each full conversion, which is exactly where I made my mistake. Saved me from having to hire a tax pro!

Quick tip for anyone fixing Form 8606 errors: Make sure you're properly accounting for any growth that happened between contribution and conversion. If your $6000 contribution grew to $6050 before conversion, that $50 is taxable in the year of conversion. I see people miss this all the time with backdoor Roth IRA calculations. Also remember that basis is tracked at the taxpayer level, not the account level. So if you have multiple traditional IRAs, they all figure into your pro-rata calculation on Form 8606 even if you're only converting from one of them.

Has anyone successfully used the IRS's "Get Transcript" online to get copies of previously filed 8606 forms? I need to see what I submitted for the last few years to fix my backdoor Roth basis calculations.

For anyone else filing corrected 8606 forms for their backdoor Roth IRA: I just went through this process and prepared a simple cover letter to attach to my corrected forms that read: "Please find enclosed corrected Forms 8606 for tax years 2020, 2021, and 2022. These corrected forms properly reflect the basis of non-deductible IRA contributions and Roth conversions that were made in each year. The original forms contained calculation errors but the corrections do not change my tax liability for any year." The IRS processed them without issue and I received confirmation letters about 8 weeks later.