Why this matters

A Roth conversion moves money from a traditional IRA or other pre‑tax account into a Roth IRA and usually creates taxable income the year of conversion. If you reported the converted amount incorrectly, your tax liability — and any refund or balance due — will be wrong. Fixing the error promptly limits interest and penalty exposure and keeps your IRS and custodian records aligned.

Step‑by‑step: how to amend

  1. Confirm the error and gather documents
  • Compare your filed return to the IRA custodian’s statements: Form 1099‑R (shows distributions) and Form 5498 (shows contributions/rollovers). Check your original Form 8606 (if one was filed) because conversions are reported there.
  • If the custodian issued a corrected 1099‑R/5498, save that document — you’ll attach or reference it when you amend.
  1. Determine the correct tax effect
  • Recalculate the taxable portion of the conversion. If your conversion involved after‑tax (basis) and pre‑tax amounts, use Form 8606 to compute the taxable portion. If you didn’t file Form 8606 originally but should have, include the completed Form 8606 with your amendment.
  1. Complete Form 1040‑X
  • Use Form 1040‑X to show the originally reported amounts, the corrected amounts, and the reason for the change. Attach corrected schedules, a corrected Form 1040 if needed, and any corrected Form 8606 and 1099‑R. The IRS explains Form 1040‑X filing and attachments on its website. (See: About Form 1040‑X: https://www.irs.gov/forms-pubs/about-form-1040x)
  1. Explain the change in plain language
  • Include a short statement explaining the error (for example: “1099‑R box 1 reported $25,000; correct amount is $15,000 due to prior‑year conversion being double‑counted”). Attach supporting custodian statements.
  1. File and pay, if necessary
  • You can e‑file amended returns for many recent tax years or mail a signed paper Form 1040‑X; check current IRS e‑file guidance. If you owe additional tax because of the correction, pay as soon as possible to reduce interest and penalties. Paying late interest generally accrues from the original due date. (See: About Form 1040‑X: https://www.irs.gov/forms-pubs/about-form-1040x)

Deadlines and timing

  • Refund claims: generally within 3 years from the date you filed the original return or 2 years from the date you paid the tax, whichever is later. For refunds, use Form 1040‑X and follow IRS deadlines. (IRS: About Form 1040‑X)
  • Processing: amended returns typically take several weeks to process — often 8–16 weeks — though times can vary.

Attachments and forms you’ll likely need

  • Corrected or original Form 1099‑R from your custodian
  • Form 8606 (Nondeductible IRAs and conversions) — attach a corrected copy if the conversion tax basis changed
  • Any corrected Form 5498 if it affects your records
  • A corrected Form 1040 or any schedules that changed

Common scenarios and examples

  • Overstated conversion: If you reported $20,000 but actually converted $10,000, filing Form 1040‑X and a corrected Form 8606 typically produces a refund for the tax overpaid.
  • Missing Form 8606: Failing to file Form 8606 when required can make the conversion look fully taxable. An amendment that adds Form 8606 may reduce the taxable amount and increase your refund.

Interest, penalties, and audits

Amending a return doesn’t automatically trigger an audit, but the IRS may review the change. If the amendment shows additional tax owed, interest and possible accuracy‑related penalties can apply; paying promptly limits those charges. If the amendment produces a refund, you must file within the refund time limits mentioned above.

When to get professional help

If your conversion involves rollover timing issues, prorated basis calculations across multiple IRAs, or multiple years of errors, consult a CPA or an enrolled agent. In my practice I’ve seen basis misallocations that require multi‑year Form 8606 reconstructions — a tax pro can help avoid repeating the mistake.

Helpful resources and internal links

Professional disclaimer

This article is educational and not individualized tax advice. Tax rules change and facts vary by case — consult your CPA, enrolled agent, or the IRS before relying on this information.

Sources

Author note: As a CPA who has handled many Roth conversion amendments, I recommend reconciling custodian documents before filing to reduce the chance of a second amendment.