You can make a backdoor Roth IRA contribution for the previous year as long as the Traditional IRA contribution reaches your custodian by the federal tax filing deadline, typically April 15, and is coded to that prior tax year. The Roth conversion itself is a separate event that follows calendar-year timing, so a contribution designated for 2025 can be converted in 2026 and will appear on your 2026 return. Keeping those two events straight is the whole trick.
The April 15 Contribution Deadline
The IRS lets you designate a Traditional IRA contribution for the previous tax year as long as the money arrives by the federal filing deadline, typically April 15 of the following calendar year.1Internal Revenue Service. Traditional and Roth IRAs Filing a tax extension does not buy extra time. The extension pushes back your Form 1040 due date, but the IRA contribution deadline stays fixed at April 15.2Internal Revenue Service. IRA Year-End Reminders
When you deposit the money, tell your custodian in writing to code it as a prior-year contribution. If you walk into your brokerage on March 10, 2026, and deposit $7,500 without specifying, the custodian will default to coding it for 2026. You want it coded for 2025 if that is the year you are targeting. The coding determines which tax year’s Form 8606 tracks the basis.
Miss April 15 and there is no workaround. Prior-year contributions cannot be made late, with or without an extension. Your only option at that point is a current-year contribution.
Who the Backdoor Is For
The strategy exists because the IRS phases out direct Roth IRA contributions at higher incomes. For 2026, the phase-out ranges are:
- Single filers: $153,000 to $168,000. Above $168,000, direct Roth contributions are prohibited.
- Married filing jointly: $242,000 to $252,000. Above $252,000, direct contributions are prohibited.
- Married filing separately: $0 to $10,000.
If your income sits within a phase-out range, you can contribute a reduced amount directly. Above the range, the backdoor is your only route into a Roth IRA. The mechanics are the same regardless: a nondeductible contribution to a Traditional IRA, followed by a conversion to a Roth IRA.3Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
The combined limit across all your Traditional and Roth IRAs is $7,500 for 2026, up from $7,000 in 2025. If you are 50 or older, the catch-up adds $1,100, bringing the total to $8,600. Your contribution also cannot exceed your taxable compensation for the year. A working spouse can fund a Traditional IRA for a non-working spouse the same way, provided the working spouse has enough compensation to cover both.4Internal Revenue Service. Retirement Topics – IRA Contribution Limits
Making the Contribution Nondeductible
The Traditional IRA contribution must be designated as nondeductible. You do not subtract it from your adjusted gross income, and you will not owe tax on it again when you convert. The nondeductible designation creates what the IRS calls basis in your Traditional IRA.
Track that basis on Form 8606 (Nondeductible IRAs), Part I. File the form with the return for the year the contribution was designated. A contribution made in March 2026 and coded for 2025 goes on the Form 8606 attached to your 2025 return.5Internal Revenue Service. Instructions for Form 8606 (2025) File it even if you have not converted yet. The IRS needs your basis on record before any conversion is reported.
High earners covered by a workplace retirement plan generally cannot deduct Traditional IRA contributions anyway, which is why the nondeductible designation fits cleanly. You are not giving up a deduction you would otherwise have gotten.
The Roth Conversion Follows Calendar-Year Timing
The conversion is a separate event and follows different timing rules than the contribution. Contributions can be backdated to a prior year; conversions are always reported in the calendar year they actually happen. You convert by asking your IRA custodian to transfer the funds from your Traditional IRA to a Roth IRA. Most brokerages handle it electronically.
The conversion can happen immediately after the contribution, even the same day. Most people do it that way to minimize any earnings that accumulate in the Traditional IRA between contribution and conversion. Those earnings, however small, become taxable income for the conversion year.
Nothing forces you to convert quickly. You could contribute in March for the prior tax year and delay the conversion until September. The delay just means more potential earnings sitting in the Traditional IRA. For a contribution designated 2025 but converted in June 2026, the conversion goes on your 2026 return. Your custodian will issue a Form 1099-R for the conversion amount.6Internal Revenue Service. Instructions for Forms 1099-R and 5498 (2025)
The Pro-Rata Rule Can Wreck the Strategy
This is where most backdoor Roth plans go wrong. Federal law requires the IRS to treat all of your Traditional, SEP, and SIMPLE IRAs as a single pool when calculating tax on a conversion. The statute is blunt: “all individual retirement plans shall be treated as 1 contract.”7Office of the Law Revision Counsel. 26 USC 408 – Individual Retirement Accounts It does not matter if the accounts are at different brokerages.
The pro-rata rule sets the taxable share of a conversion based on the ratio of pre-tax dollars to total dollars across that pool, measured by the total value of all your Traditional IRAs on December 31 of the conversion year.5Internal Revenue Service. Instructions for Form 8606 (2025)
Here is what that looks like. You make a $7,500 nondeductible contribution, but you also have a rollover IRA from an old job holding $92,500 of pre-tax money. Your total IRA balance is $100,000, and 92.5% of it is pre-tax. When you convert the $7,500, you cannot cherry-pick just the nondeductible dollars. Instead, 92.5% of the conversion ($6,937) is taxable as ordinary income.
How To Clear the Pro-Rata Problem
The most effective fix is rolling your pre-tax IRA balances into an employer plan like a 401(k) or 403(b) before December 31 of the conversion year. That removes the pre-tax dollars from the aggregated IRA pool and leaves only your nondeductible contribution behind. When you convert, almost nothing is taxable.
Check with your plan administrator first. Not every 401(k) accepts incoming rollovers from IRAs, and some restrict the types of money they will take. If you cannot move the pre-tax funds, you have to accept the tax hit on the pro-rata portion or reconsider whether the conversion is worth doing at all.
Reporting Across Two Tax Years
A prior-year backdoor Roth splits reporting across two returns. Getting the forms right protects the nondeductible basis you established.
The Prior Year’s Return
File Form 8606, Part I, with the return for the year the contribution was designated. This is where you report the nondeductible amount and establish your basis. A contribution made in February 2026 for tax year 2025 goes on the 2025 return.5Internal Revenue Service. Instructions for Form 8606 (2025)
Your custodian will issue a Form 5498 showing the contribution amount and the year it was designated. Box 1 captures prior-year Traditional IRA contributions made through April 15.8Internal Revenue Service. Form 5498, IRA Contribution Information Keep it to reconcile with your Form 8606.
The Conversion Year’s Return
File Form 8606, Part II, with the return for the year the conversion took place. Part II calculates the taxable portion of the conversion under the pro-rata formula, using your total IRA balances as of December 31.5Internal Revenue Service. Instructions for Form 8606 (2025)
The Form 1099-R for the conversion year will typically show the full conversion amount in both box 1 and box 2a with a distribution code indicating a Roth conversion.6Internal Revenue Service. Instructions for Forms 1099-R and 5498 (2025) Do not panic when the 1099-R makes the whole amount look taxable. Form 8606 is where the nondeductible basis is applied.
If You Already Filed Without Form 8606
If you filed a prior year’s return without attaching Form 8606, you are not permanently locked out. You can file Form 1040-X with a corrected or newly attached Form 8606 to establish or fix your nondeductible basis, as long as you are within the time limit for amended returns. The IRS can also assess a $50 penalty for each failure to file Form 8606, though you can request a waiver by showing reasonable cause.5Internal Revenue Service. Instructions for Form 8606 (2025)
Skipping the form is expensive if left unfixed. The IRS presumes your entire Traditional IRA balance is pre-tax without a documented basis, so you end up paying tax on the conversion of money you already paid tax on. The longer you wait, the harder it gets to reconstruct that basis from old statements. If you have been making nondeductible contributions for years without tracking them, plan on filing Form 8606 for each year you missed.
One more penalty to know about: excess contributions carry a 6% excise tax for every year they remain in the account. You can avoid it by withdrawing the excess and its earnings before the filing deadline, including extensions.9Office of the Law Revision Counsel. 26 U.S. Code 4973 – Tax on Excess Contributions to Certain Tax-Favored Accounts and Annuities The excess most often shows up when a January-through-April contribution gets coded to the wrong year, which is why confirming the year designation in writing at the time of deposit is worth the extra minute.