Forgot or Made an Error on Form 8606? Here’s How to Undo the Damage

If you forgot to file Form 8606 or realize you made a mistake, don’t panic. But do pay attention. This often-overlooked tax form trips up many taxpayers, specifically high earners using the backdoor Roth IRA strategy or those filing as married filing separately (MFS). If you left it out or filed it incorrectly, you could be facing unnecessary taxes, missing documentation of your IRA basis or worse: the IRS treating your entire IRA like it’s fully taxable. Keep reading to learn how to fix IRS Form 8606.

What is IRS Form 8606 and why should you care?

IRS Form 8606 reports non-deductible contributions to traditional IRAs, along with Roth conversions and distributions involving after-tax money. Basically, it’s how you tell the IRS, “Hey, I already paid taxes on this money, so don’t tax me again.”

While some people contribute to a traditional IRA for an upfront tax deduction, others (e.g., high earners who exceed the Roth IRA income limits) use it to make after-tax contributions with the goal of converting them to a Roth IRA later. This is known as a backdoor Roth IRA, and it hinges on accurate Form 8606 reporting.

Form 8606 plays a key role in:

Establishing your IRA basis (so you’re not taxed twice).
Reporting backdoor IRA conversions (important for high-income households).
Showing the IRS your conversion was tax-free (unless the pro-rata rule applies).

Note the pro-rata rule kicks in when you have both pre-tax and after-tax money in your IRA, including traditional, SEP and Simple IRAs. In which case, your conversion isn’t entirely tax-free. It’s partially taxable based on the ratio of after-tax to total IRA balances. Form 8606 helps calculate and document that properly.

Here’s what IRS Form 8606 looks like:

Source: IRS Form 8606

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What happens if you forgot to file Form 8606?

The consequences of forgetting to file Form 8606 can range from annoying to expensive. If you don’t report your non-deductible IRA contributions or Roth conversions correctly, the IRS may assume your entire traditional IRA is pre-tax. This can lead to double taxation, meaning you could be taxed again on money you already paid taxes on when you convert or withdraw funds in the future. To make matters worse, neither the IRS nor your tax preparer will have a record of your basis, increasing the risk of costly errors.

The IRS may not catch the mistake right away. But when they do, it can snowball quickly. You might receive IRS notices that bring confusion and stress. You could even face a penalty for each missed form, unless you can show reasonable cause for the omission.

You’re not alone: Common Form 8606 mistakes

If you forgot to file Form 8606, you aren’t the first and you certainly won’t be the last. Here are some of the most common mistakes involving Form 8606:

Completed a backdoor Roth conversion and didn’t file Form 8606. This is by far the most frequent error. Without Form 8606, the IRS assumes the entire conversion is taxable, even if it should have been tax-free.
Filed Form 8606 but reported it incorrectly. Maybe you paid taxes on a Roth conversion that you didn’t need to or failed to track your IRA basis from non-deductible contributions properly. Either way, this can lead to overpaying taxes or IRS confusion.
Married filing separately and contributed directly to a Roth. If your income was over $10,000, you weren’t eligible to contribute directly to a Roth IRA in the first place. If you catch the mistake by October 15 of the following year, you can recharacterize your Roth contribution and file Form 8606 to report the conversion correctly. Otherwise, you’ll need to remove the excess contribution and any earnings to avoid penalties.
Tax preparer overlooked Form 8606. Not all tax preparers understand backdoor Roths or the nuances of married filing separately. If your preparer didn’t ask about nondeductible contributions, they may have missed the form entirely.
DIY tax filers didn’t know Form 8606 was needed. IRS instructions aren’t always crystal clear, and tax software doesn’t always prompt you. Many DIYers skip the form simply because they don’t realize it applies to them.

The good news is that whether you forgot to file Form 8606 or just made a mistake, there are ways to fix it and get back on track with the IRS.

How to file Form 8606 for previous years

If you forgot to file Form 8606 in a previous year, you can (and should) still fix it. The best approach depends on your specific situation and how thorough you want to be.

Option 1: Amend your tax return and include Form 8606

Amending your tax return is the safest and most comprehensive method for fixing this mistake. You’ll need to file IRS Form 1040-X for the year in question and include the missing Form 8606. This ensures the IRS officially associates your IRA basis or conversion details with the right tax year and avoids confusion down the line.

This option is considered best practice as amending the return gives you the most complete paper trail. It’s especially important if taxes were overpaid or reported incorrectly.

Option 2: Mail the missing Form 8606

Some tax professionals take a lighter-touch approach and recommend mailing the standalone Form 8606 for the missed year, along with a brief cover letter explaining the oversight. This is faster and may be fine if your tax return didn’t need any other changes. But there’s a risk the IRS won’t fully process it or link it to your original return.

How to correct Form 8606 if you made a mistake

If you discover an error on a previously filed Form 8606, you can correct it by amending your tax return and submitting a corrected Form 8606 for the same tax year. Here’s how:

Fill out Form 1040-X for the year the error occurred.
Attach a corrected Form 8606 reflecting the accurate contribution, conversion or distribution details.
Include a brief explanation of the mistake and your correction.
Mail both forms to the IRS address listed for your state in the 1040-X instructions.

Let’s say you accidentally reported your Roth conversion as taxable when it should have been tax-free. You’ll want to address this error as soon as possible to correct the IRS’s records and your own basis tracking as it’ll impact future conversions and withdrawals. It can also help you claim a refund if your initial mistake caused you to pay unnecessary taxes.

Even if the mistake doesn’t change your tax due, an incorrect IRA basis can create bigger problems years down the line. Amending now ensures the IRS has an accurate record and reduces the risk of double taxation in the future.

Form 8606: Penalties and processing times

If you forgot to file Form 8606 when required to, the IRS may assess a $50 penalty per missed form (and a $100 penalty for overstating nondeductible contributions). However, the penalty can be waived if you can show reasonable cause.

For example, you might be able to dodge the penalty if you were relying on a tax preparer who missed it or were dealing with a serious illness, death or unavoidable absence when your taxes were filed. To request a waiver, include a short written explanation when you file the late form or amended return. That said, it’s best to be prepared to pay the penalty.

Also keep in mind that it can take months for an amended tax return to be processed, especially during peak tax season. If you’re only mailing in a standalone Form 8606, the turnaround might be faster. But there’s no official timeline and you may not get confirmation unless the IRS later reaches out or updates your account transcript.

How SLP Wealth can help correct and avoid tax filing mistakes

If you’re not sure whether you filed Form 8606 correctly (or at all), the SLP Wealth team can help get clarity and take action before it becomes a bigger problem.

We’ll help identify past filing issues, fix what needs fixing and avoid unnecessary taxes and penalties in the future. Even better, we’ll work with you to build a proactive tax strategy that keeps you on track for your retirement and financial goals.