Form 8606 for a Backdoor Roth IRA: How to Report It

Start with the actual transactions, not the date you opened the IRA or the date the brokerage sent a form. A traditional IRA contribution can be designated for the previous tax year if it is made by the applicable contribution deadline and you meet the contribution rules. A Roth conversion is reported for the calendar year in which the conversion was completed.

So a contribution you make in February 2026 for tax year 2025 and a conversion you complete in May 2026 are not one 2025 transaction. The nondeductible contribution belongs in the 2025 basis reporting. The conversion belongs in 2026 reporting. If you made both during 2025, the same-year reporting would be different.

Keep two date labels next to your records: “contribution for tax year” and “conversion completed on.” The IRS’s 2025 Form 8606 instructions and Form 8606 make that distinction explicit. You still have to account for the IRA balances and other transactions that affect the conversion-year calculation.

• The traditional IRA contribution confirmation, showing the amount, the actual deposit date, and the tax year for which it was designated. Keep the custodian record even if Form 5498 has not arrived.
• The Form 5498 for the contribution year when available. It helps corroborate the IRA contribution, but custodians may furnish it after the normal April individual income-tax filing date.
• The Form 1099-R for the calendar year in which the Roth conversion was completed, along with the custodian’s conversion confirmation. The amount distributed and the final taxable amount need not be the same.
• Your most recent completed Form 8606 and any intervening IRA transaction records that affect basis. A prior-year basis amount is not the same thing as the total you have ever converted into a Roth IRA.
• The relevant December 31 traditional, SEP, and SIMPLE IRA statements, plus any other IRA distributions or outstanding rollovers that the applicable form instructions require.

If you and your spouse file jointly, keep each person’s IRAs and nondeductible basis separate. When both spouses have reporting obligations, the IRS calls for a separate Form 8606 for each spouse. A joint tax return does not create one combined household IRA basis.

Your contribution confirmation establishes the amount and designated tax year; Form 1099-R reports the conversion-year distribution; the prior Form 8606 helps establish how much traditional IRA basis remains. You need all of those facts, along with the applicable IRA balances and other transactions, to check the taxable portion.

On the finalized 2025 Form 8606, line 1 generally reports your nondeductible traditional IRA contributions for 2025, including eligible contributions made in early 2026 and designated for 2025. Line 2 generally brings in prior traditional IRA basis, as adjusted under the instructions. The form then handles whether there was a 2025 distribution or conversion. The 2025 instructions explain those branches rather than treating every filer as the same case.

For example, someone under age 50 who made an eligible, entirely nondeductible $7,000 contribution in February 2026 specifically for 2025, with no prior basis and no 2025 traditional IRA distribution or conversion, would generally report the $7,000 on the 2025 Form 8606 and carry it into the form’s remaining basis. The contribution itself does not create a 2025 Roth conversion.

The 2025 Form 8606 instructions are the controlling reference for those line numbers. Do not copy them into a 2026 filing screen without checking the final 2026 instructions when available. Eligibility and the deductible-versus-nondeductible treatment need their own check against the IRS IRA contribution rules.

Where Do Prior-Year IRA Basis Amounts Go?

Here is a common trap. The balance in a traditional IRA is not automatically your basis, and your lifetime Roth contributions are not your traditional IRA basis either. The relevant basis is the previously taxed traditional IRA amount remaining after prior conversions, distributions and other adjustments.

Use the most recent properly prepared Form 8606 and the IRS basis chart to establish the starting amount. For finalized tax-year 2025, line 14 shows remaining traditional IRA basis that may be relevant in later years, and line 2 generally carries prior basis into the calculation. Exceptions and adjustments matter, especially when an IRA has had earlier distributions or changes of ownership.

If the old form is missing, do not invent the basis figure just to make tax software produce the answer you expected. Reconstruct it from prior filed returns and IRA records, then determine what needs correction before proceeding.

For the finalized 2025 Form 8606, line 8 captures the amount converted from traditional IRAs to Roth IRAs in 2025 for the relevant calculation. Part II then reports the conversion and its nontaxable and taxable portions, including the line 16 through 18 results as instructed. The 2025 Form 1040 distinguishes total IRA distributions from taxable IRA distributions. The conversion-year form and return must agree under the actual facts.

A plain example helps: if an eligible taxpayer has documented nondeductible basis equal to the entire amount converted in the same year, and no other included IRA balances, distributions, earnings or complications, the taxable conversion amount may be zero. That is a conditional result, not what happens automatically every time someone says “backdoor Roth.”

What Changes When You Have Other Traditional IRA Balances?

The IRS pro-rata calculation can include relevant traditional, SEP, and SIMPLE IRA balances held by the same individual. It may also account for other distributions and outstanding rollovers under the year’s instructions. You cannot generally choose to convert only the nondeductible dollars from one traditional IRA while excluding other relevant traditional IRA assets from the calculation.

If you have those balances, stop before using the clean example. Review the Roth conversion pro-rata rules and the broader backdoor Roth IRA preflight. The year-end values and distribution history can change how much of a conversion is taxable even when the new contribution itself was nondeductible.

The taxable portion is income for the return’s tax calculation. It is not the tax bill. A $500 taxable conversion portion does not mean you owe $500 of additional income tax; your total return and applicable rates determine the tax cost.

For the final 2025 Form 8606, Part I would show line 1 $7,000, line 2 $0, line 3 $7,000, line 5 $7,000, line 6 $0, line 7 $0, line 8 $7,010, line 9 $7,010, line 10 approximately 0.9985735, line 11 $7,000, line 13 $7,000 and line 14 $0. Part II would show line 16 $7,010, line 17 $7,000 and line 18 $10 taxable. Form 1040 lines 4a and 4b would generally show $7,010 and $10 respectively, assuming no other IRA activity.

Don’t round the line 10 fraction too early: the instructions say at least three decimal places, and carrying additional precision prevents a false basis result in this example. The Form 1099-R records the distribution, but its box 7 code depends on the transaction and age. These numbers are illustrative, not a substitute for checking all IRA balances and the actual form-year instructions.

Assume the taxpayer has no prior traditional IRA basis, no other relevant traditional/SEP/SIMPLE IRA assets, no other traditional IRA distributions, no outstanding rollovers, and no adjustment that changes the basis computation. Those facts are important; this is not a universal $5 tax rule.

Which Tax Forms Belong to 2025?

The $7,000 contribution is designated for tax year 2025. On the finalized 2025 Form 8606, it generally appears as a nondeductible contribution and, with no 2025 conversion or distribution in this example, creates remaining traditional IRA basis to carry forward. The 2025 Form 8606 does not report the May 2026 conversion.

That is why receiving no 2025 Form 1099-R for the May 2026 conversion is not, by itself, evidence that the custodian forgot to report it. The distribution did not take place in 2025.

Which Tax Forms Belong to 2026?

The $7,005 conversion occurred in May 2026, so it belongs in the 2026 tax-year Roth conversion reporting, normally with a 2026 Form 1099-R supplied for that transaction year. The documented $7,000 remaining nondeductible basis from the prior year is an input to the applicable conversion-year Form 8606 calculation.

Under the strict assumptions above, the conversion contains $7,000 of previously taxed traditional IRA basis and $5 of gain. The taxable portion would generally be $5. That is $5 added to the taxable calculation, not a $5 bill. If the taxpayer also has other relevant IRA assets or transactions, this simple result can change.

As of October 2026, the available 2026 Form 8606 instructions were still marked draft, not for filing. Recheck the final 2026 instructions before using exact line numbers or submitting the 2026 return.

Start with the prior Form 8606. Does its remaining traditional IRA basis, after legitimate adjustments, support the basis entered on the next year’s form? Then check the contribution confirmation. Was it a 2025 contribution made in 2026, or a 2026 contribution? The year printed on a bank statement is not always the contribution tax year.

Next look at the conversion confirmation and the 1099-R. They should tell the story of the distribution in the actual conversion year. Bring in the relevant December 31 IRA balances and any other distributions or outstanding rollovers. Only then compare the resulting Form 8606 nontaxable/taxable allocation with the IRA amounts on Form 1040.

For our hypothetical example, it is entirely reasonable to see $7,000 of 2025 nondeductible basis, a 2026 gross Roth conversion of $7,005, and generally $5 as the taxable conversion portion when the stated assumptions hold. Those numbers are not supposed to be identical. They answer different questions.

What Should Match and What Might Legitimately Differ?

The contribution year on Form 5498 and the designated year in the custodian’s contribution record should be consistent. The conversion date in your transaction history should correspond to the calendar year of the distribution reported on the 1099-R. The prior basis carried into the conversion-year calculation should be explainable from prior completed Forms 8606 and intervening transactions.

But do not force the 1099-R gross distribution to equal the taxable IRA amount on Form 1040. One may show the whole amount moved, while the other reflects the taxable result after basis allocation. Nor should you assume Form 5498 must already be in your hands by the tax-filing date. That form’s furnishing timetable can differ from when you need to prepare the return.

If a number disagrees, ask a sharper question: Is the contribution in the wrong year, is a prior basis amount missing, did another IRA balance enter the pro-rata calculation, or was a transaction categorized incorrectly? Changing a single software answer without finding the underlying difference can make the return look neater while leaving the mistake in place.

Missing Form, Correct Taxable Income

Suppose you failed to include a Form 8606 for an earlier nondeductible contribution, yet the rest of that year’s tax return did not misstate taxable IRA income. You still need to establish and report the basis properly. The IRS 2025 Form 8606 instructions discuss filing obligations and how changes may be handled. Do not assume that simply attaching a missing form to any later return automatically cures the earlier filing, or that every situation requires the same amended-return procedure.

If the missing Form 8606 did not change taxable income, check the IRS instructions for filing a signed standalone prior-year Form 8606. If the original return reported the wrong taxable IRA amount, Form 1040-X may also be necessary. The IRS lists a $50 penalty for not filing a required Form 8606 and a $100 penalty for overstating nondeductible contributions, with reasonable-cause exceptions. Keep the earlier return, IRA basis records and contribution documentation together.

Incorrect Taxable Income or Missing Basis

If a conversion was treated as entirely taxable despite substantiated basis, or prior basis was counted twice, the filed taxable amount may be wrong. Use the affected year’s correction rules to determine whether a corrected Form 8606 and Form 1040-X are needed.

Don’t guess your way through that repair. Reconcile the transactions first, identify the earliest return with an unsupported number, and check what flowed into later returns. A mistake in the basis carried forward can affect more than one filing year. The IRS instructions discuss Form 1040-X and revised Form 8606 in applicable amendment circumstances; they do not establish one universal fix for every omission.

An excess or ineligible IRA contribution is a different issue. If the records reveal one, that calls for separate contribution-correction rules rather than treating it as a Form 8606 checkbox problem.

1. Write down the contribution’s designated tax year and the actual calendar year of every Roth conversion.
2. Confirm whose IRA it was. On a joint return, check each spouse’s IRA basis and Form 8606 separately when required.
3. Locate the prior filed Form 8606 and verify the remaining nondeductible basis, including any adjustments.
4. Match the contribution confirmation and Form 5498 when available, then the 1099-R and conversion confirmation for the transaction year.
5. Verify the applicable December 31 traditional, SEP, and SIMPLE IRA values, other distributions and outstanding rollovers before accepting the pro-rata result.
6. Compare the year-specific Form 8606 taxable and nontaxable calculation with the Form 1040 IRA entries. A gross distribution and taxable income can properly differ.
7. If something is missing or inconsistent, identify the source of the discrepancy before changing the return. Seek qualified tax help when basis cannot be reconstructed or filed taxable income may be incorrect.
8. Save the final returns, Forms 8606, custodial confirmations, and support for basis. You’ll want that history when the next contribution or conversion comes around.

One last practical point: a successful account transfer does not, by itself, prove the tax reporting is right. The evidence is the set of records and how the amounts reconcile. Keep those, and the next year’s filing is much easier to check.

For broader backdoor Roth eligibility and IRA-balance planning, see the backdoor Roth IRA guide. For the tax mechanics behind mixing pretax IRA money with basis, see the Roth conversion pro-rata rules. For the actual form-year reporting requirements, use the IRS’s Instructions for Form 8606.

If you want more plain-English explanations of the financial decisions behind the forms, the Financial Clarity Newsletter is available here.