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Deductible vs. Nondeductible IRA Contributions: A Basis Decision Checklist

Published by Moss Ladder · Updated November 2, 2026 · Editorial policy

Executive summary

An IRA deposit, an IRA deduction and IRA basis are three different records. Confusing them can make a Roth conversion look either more taxable or less taxable than it really is. This guide follows one contribution from the funding instruction to the tax return, with a decision checklist for identifying the portion that actually becomes nondeductible basis. The examples assume an eligible regular contribution; they do not determine eligibility from an account statement alone.

Educational guidance for ordinary scenarios. Check the official form's year and filing branches and obtain advice for your actual records.

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Answer contribution permission before deduction eligibility

Begin with the contribution year, the owner's age, taxable compensation and other regular IRA contributions for that same year. A traditional IRA account accepting a deposit does not establish that the deposit is permitted. The annual traditional and Roth IRA contribution limits are shared, and the compensation rule can matter even when a taxpayer has substantial investment income. A joint return can allow a spousal IRA contribution under the applicable compensation rules, but the account still belongs to one individual.

Only after that first question should you determine the deduction. Workplace retirement-plan coverage, filing status and modified adjusted gross income can restrict a traditional IRA deduction. Those tests are different from the direct Roth contribution income test. Do not assume that being unable to deduct a traditional contribution means being unable to make it, or that an accepted contribution is automatically deductible. Write the two decisions on separate lines in the workpapers and identify the tax-year source used for each.

Use the filed deduction, not the funding account, to identify basis

A bank transfer from an ordinary checking account does not by itself create nondeductible IRA basis. The same transfer could fund a contribution that is deducted on the return, a contribution that is nondeductible, or a contribution that later needs correction. The tax treatment must be reconciled with the return. Calling the checking account money after tax is not enough: a deduction can reverse that initial income-tax burden, so counting both the deduction and full contribution as basis would duplicate the benefit.

For an eligible contribution that is only partly deducted, separate the deducted portion from the nondeductible portion. For example, suppose a $6,000 contribution is permitted and the correctly prepared return allows a $2,000 deduction. The remaining $4,000 is the potential nondeductible amount to report, subject to the actual instructions and any corrections. Save the calculation supporting the partial deduction. A brokerage contribution confirmation normally establishes the deposit and designated year, not the deduction actually claimed on your return.

Worked comparison: the same deposit, three return treatments

This comparison holds the permitted $6,000 deposit constant and changes only the deduction on a correctly prepared return. It deliberately does not assign an income threshold or assume workplace coverage. The point is to reconcile the contribution to the deduction before deciding what belongs in the basis record. An excess contribution or a contribution later recharacterized needs a separate analysis rather than this ordinary subtraction.

Illustrative contribution-to-basis reconciliation
Permitted contribution	Deduction claimed	Nondeductible portion	Evidence to retain
$6,000	$6,000	$0	Deduction calculation and filed return
$6,000	$2,000	$4,000	Partial-deduction worksheet and Form 8606
$6,000	$0	$6,000	Nondeductible contribution reporting and confirmation

Connect the nondeductible amount to Form 8606

Form 8606 reports nondeductible traditional IRA contributions and tracks basis used or retained under its applicable rules. A contribution for the current tax year generally belongs with the current-year contribution information, while previously unrecovered basis belongs with the prior-basis information. Do not enter the same contribution in both places merely because a custodian form and an earlier workpaper each mention it. Use the last applicable Form 8606 and review any intervening transactions before carrying an amount forward.

Timing creates another distinction. A contribution made after December 31 for the preceding tax year can be reportable for that contribution year while still being unavailable to shelter an earlier distribution under the ordinary allocation. Keep the actual deposit date as well as the designated contribution year. If there is no distribution, the official form has a carryforward branch instead of a requirement to manufacture conversion lines. A planning allocation display and the lines required on the filed return are not always identical.

Explain why a nondeductible contribution does not make a conversion entirely tax free

After identifying basis, inventory the owner's applicable traditional, SEP and SIMPLE IRA balances and relevant annual distributions. The pro-rata calculation can allocate that basis across a conversion and other distributions. It does not reserve all basis for the specific account that received the nondeductible contribution. Moving the deposit to a new brokerage account, or converting it before touching another IRA, does not by itself remove the other IRA from the owner's annual pool.

For a separate illustration, assume $4,000 documented available basis, a $4,000 conversion and $12,000 applicable year-end IRA value, with no other adjustments. The pool is $16,000, the tax-free proportion is 25%, and the conversion uses $1,000 basis. The other $3,000 of the conversion is taxable and $3,000 basis remains. This is an allocation consequence, not proof that the original contribution should have been deducted. Change the deduction decision only when the actual return facts support it.

Resolve conflicting documents before repeating the workflow

Suppose a personal spreadsheet calls a contribution nondeductible but a filed return appears to deduct it. Do not choose whichever description produces the lower conversion tax. Retrieve the full return, the deduction worksheet, the contribution confirmation and any later amendment. Determine whether the spreadsheet was a planning note, whether the return used a partial deduction, or whether an actual error requires correction. Keep the unresolved amount explicitly marked unknown while you gather evidence.

A corrected custodian form does not necessarily correct a filed deduction, and an amended return does not automatically update a personal basis tracker. Maintain a short correction log showing which document changed, which year was affected and whether later carryforwards were reviewed. If an earlier error changes taxable distributions or tax due, a qualified preparer should determine the filing procedure. The website's record tools can organize that evidence, but they cannot decide whether a historic deduction was legally available.

Prepare a contribution-to-return checklist

For each year, retain a row with the owner, contribution year, actual funding date, gross contribution, other regular IRA contributions, allowed deduction, nondeductible amount and filing evidence. Add a reference to the statement or confirmation rather than storing account credentials in the calculator. If a contribution was returned or recharacterized, flag the row and preserve the custodian's completed transaction documents. That prevents a later reviewer from treating an abandoned plan as a completed nondeductible contribution.

Before the next conversion, reconcile the ending basis to the next opening basis and explain every difference. Ask your preparer whether workplace coverage, compensation, a filing-status change or a corrected contribution affects the earlier classification. Then use the allocation calculator only after the basis amount is supported. A useful final check is to describe the contribution, deduction and basis in three separate sentences. If those sentences conflict, resolve the record problem before relying on a conversion estimate.

About the publisher: Moss Ladder

Moss Ladder owns and publishes RothProRata.com, an independent educational website about IRA basis, Roth conversions and Form 8606. The guides connect official sources with invented examples, document checklists and browser-local planning tools.

AI-assisted tools help prepare explanations and software. Numerical allocation examples state their assumptions and are checked with automated calculations. These engineering checks do not constitute independent CPA or Enrolled Agent review, and no professional tax credential is claimed.

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Source year and transaction type matter. Citations support the explanation; they do not imply government endorsement.