How do I correct my IRA basis? In 2009, my form 8606 carried forward the wrong amount. And from 2015, I did not file form 8606. How do I fix for TY2025?

[paulalbertson]

Do I need to file a 1040-X to amend every affected return? Or can I simply report the correct basis in my 8606 for TY2025 and attach an explanatory letter?

[fanfare]

did you take any action in 2025 requiring 8606? in that case you can correct the Line 2.

Do not attach explanatory letters to 1040 unless instructed by IRS.

Why is the basis wrong.? did you pay the correct tax in 2014.? in 2009?

How big is the basis error compared to the total value of IRA? It may be miniscule tax effect.

@paulalbertson 

[paulalbertson]

Thank you, fanfare.

I hired a tax service in 2014, and they calculated a basis that was out of step with, and significantly higher than, my previous returns. I did not think to question it. I had been making nondeductible contributions to a Traditonal IRA, which did not affect the taxes owed — i.e., I paid the correct tax in 2014.

In 2025, I started converting to Roth, which will require an 8606 to report the conversion — and to correct my basis.

Question: Can you share the source for your recommendation to not attach an explanatory letter unless instructed by the IRS? I’ve heard otherwise.

Thanks again.

[fanfare]

As I mentioned above, this is your chance to enter the correct basis on 2025 Form 8606.

If IRS has any issues, they will request supporting documentation which you should have ready in your own files.

IRS is unlikely to complain if you are correcting downward to a lower basis.

@paulalbertson