Many taxpayers assume that once they contribute money to a Traditional IRA, every future withdrawal will be taxable. Others believe that because they already paid income tax before making a contribution, the IRS shouldn't tax the money again.

Both assumptions can be misleading.

The U.S. tax system is designed to prevent taxpayers from paying tax twice on the same after-tax contribution. However, this protection only works when the contribution is properly reported and tracked. That's where Form 8606 becomes important.

If Form 8606 is not filed when required, the IRS may have no record that part of your IRA consists of after-tax money, increasing the risk of double taxation.

What Does "Double Taxation" Mean?

Double taxation occurs when the same dollars are taxed more than once.

For Traditional IRAs, this concern arises when a taxpayer makes nondeductible (after-tax) contributions and later withdraws money from the account.

If those after-tax contributions are not properly tracked, the entire distribution may appear taxable, even though part of it has already been taxed in the year it was contributed.

Why Doesn't This Happen With Every IRA?

The answer depends on how the contribution was treated when it was made.

Deductible Traditional IRA Contribution

A deductible contribution reduces taxable income in the year it is made.

Because no income tax was paid on that contribution, it is generally taxed when distributed during retirement.

This is not double taxationβ€”it is simply deferred taxation.

Nondeductible Traditional IRA Contribution

A nondeductible contribution is made with after-tax dollars.

Since income tax has already been paid, that portion should not be taxed again when withdrawn.

Instead, only the earnings and any pre-tax amounts are generally taxable.

What Is IRA Basis?

IRA basis is the total amount of after-tax contributions that have not yet been recovered tax-free.

Think of it as your investment in the IRA.

Each time you take a distribution, a portion of your basis is recovered without additional tax, while the remaining basis continues to be tracked until fully used.

How Does the IRS Keep Track?

The IRS relies on Form 8606, Nondeductible IRAs.

This form records:

  • Nondeductible Traditional IRA contributions
  • Remaining IRA basis
  • Roth IRA conversions
  • Taxable and nontaxable portions of certain IRA distributions

Without Form 8606, neither the taxpayer nor the IRS has an official record of the after-tax basis.

What Happens If You Forget to File Form 8606?

Failing to file Form 8606 can create several problems:

  • Your IRA basis may not be documented.
  • Future IRA distributions may appear fully taxable.
  • You may pay tax on money that was already taxed.
  • Reconstructing basis years later can be difficult if records are missing.

Keeping copies of Form 8606 with your permanent tax records is essential.

Does Form 1099-R Prevent Double Taxation?

Not necessarily.

Form 1099-R reports the distribution from your IRA, but the financial institution may not know whether you have after-tax basis from prior years.

As a result, the taxable amount shown on Form 1099-R may not reflect your actual tax liability.

Form 8606 is often needed to calculate the correct taxable amount.

What Is the Pro-Rata Rule?

The IRS does not allow taxpayers to withdraw only their after-tax contributions first.

Instead, every distribution from Traditional, SEP, and SIMPLE IRAs is treated as containing both:

  • Taxable pre-tax funds
  • Nontaxable after-tax basis

This is known as the pro-rata rule, and it ensures that basis is recovered proportionately over time.

Can Everyone File Form 8606?

No.

Form 8606 is generally required only in specific situations, such as:

  • Making a nondeductible Traditional IRA contribution
  • Receiving a distribution from a Traditional IRA that contains basis
  • Converting a Traditional IRA to a Roth IRA
  • Receiving certain Roth IRA distributions

Taxpayers who have only deductible Traditional IRA contributions may never need to file Form 8606.

Tips to Avoid Double Taxation

  • Determine whether your Traditional IRA contribution is deductible.
  • File Form 8606 whenever required.
  • Keep every copy of Form 8606 permanently.
  • Review Form 1099-R carefully before filing your return.
  • Inform your tax preparer if you have made after-tax IRA contributions in prior years.

Frequently Asked Questions

Can the IRS really tax the same IRA contribution twice?

The tax law is designed to prevent this, but if after-tax contributions are not properly reported and documented, the taxable portion of a distribution may be overstated.

Does every Traditional IRA have basis?

No. Basis exists only if the taxpayer has made nondeductible contributions or rolled certain after-tax amounts into the IRA.

Does Form 1099-R show my IRA basis?

Generally, no. Form 1099-R reports the distribution but usually does not track a taxpayer's cumulative IRA basis.

How long should I keep Form 8606?

Keep every Form 8606 for as long as you have any remaining IRA basis. Many tax professionals recommend retaining copies permanently because basis can carry forward for many years.

Final Thoughts

Paying tax twice on the same IRA contribution is not the intention of the tax law. The IRS provides Form 8606 to ensure that after-tax contributions are properly tracked and recovered tax-free over time. Understanding your IRA basis, maintaining accurate records, and filing the required forms can help prevent unnecessary tax and make retirement distributions easier to report correctly.