Can You Convert a Nondeductible IRA to a Roth? (w/Examples) + FAQs

Quick Answer: Yes. For tax year 2025, anyone can convert a nondeductible traditional IRA to a Roth IRA — there is no income limit on conversions. You owe tax only on pre-tax amounts and earnings, not on your after-tax basis. The IRS “pro-rata rule” decides how much is taxable.

This article reflects federal rules as of June 2026 and covers tax years 2025 and 2026. State rules are addressed in a dedicated section below. Tax law changes — confirm current figures before you file.

You put money into a traditional IRA, did not deduct it, and now you want that money growing tax-free in a Roth. The good news is the door is wide open: converting is legal for everyone, regardless of income. The catch is that the IRS does not let you cherry-pick only your after-tax dollars to move — and missing that point is where people get a surprise tax bill.

This matters most for high earners. The Roth IRA itself has an income cutoff: for 2025, single filers are fully phased out at a modified adjusted gross income (MAGI) of $165,000, and married-filing-jointly couples at $246,000. According to Investment Company Institute data, roughly 40% of U.S. households own an IRA, and many high earners use the nondeductible-then-convert path — the “backdoor Roth” — as their only way into a Roth. Done wrong, it triggers tax that should never have been owed.

Here is what you will learn:

💰 How the pro-rata rule decides exactly how much of your conversion is taxed.
🧾 How to report the whole thing on Form 8606 so the IRS does not double-tax you.
🚪 How the “backdoor Roth” works step by step, and who it is built for.
⚠️ The single mistake — leftover pre-tax IRA money — that wrecks most conversions, and how to fix it.
🗺️ Whether your state taxes the conversion as income (federal and state rules differ).

What a Nondeductible IRA Actually Is

A nondeductible IRA is not a separate account type. It is a regular traditional IRA that holds contributions you did not deduct on your tax return. You paid tax on that money already, so the IRS calls it your basis — money the government has no further claim on.

You end up with nondeductible contributions for one of two reasons. Either you earned too much to deduct a traditional IRA while covered by a workplace plan, or you contributed on purpose with a plan to convert later. For 2025, if you are covered by a 401(k) at work, your traditional IRA deduction phases out between $79,000 and $89,000 of MAGI for single filers, and between $126,000 and $146,000 for married filing jointly, per IRS Publication 590-A. Above those ranges, the contribution is allowed but not deductible.

The consequence of not tracking that basis is real money. If you never tell the IRS you already paid tax on those dollars, you will pay tax on them again when you convert or withdraw. The fix is a single form — Form 8606 — filed for the year you make the nondeductible contribution. A common misconception is that you only file Form 8606 the year you convert. You actually file it the year you contribute nondeductible money, and the year you convert. What to do about it: file Form 8606 every year you have nondeductible activity, and keep every copy permanently.

The Backdoor Roth, Explained Simply

The backdoor Roth IRA is not a special account either. It is a two-step move: you make a nondeductible contribution to a traditional IRA, then convert that money to a Roth IRA. It exists because Congress capped who can contribute directly to a Roth by income, but in 2010 it removed the income cap on conversions. The back door was left open on purpose.

The strategy fits high earners who are locked out of a direct Roth contribution. For 2025, the contribution limit is $7,000, or $8,000 if you are age 50 or older, per IRS guidance. For 2026, the limit rises to $7,500, or $8,600 for those 50 and older, as the IRS announced in November 2025. You contribute that amount nondeductibly, then convert it.

The consequence of skipping the back door, if you are over the income line, is no Roth at all — your retirement savings stay in taxable or pre-tax accounts. A frequent misconception is that the backdoor Roth is a loophole the IRS frowns on. It is not; the IRS has repeatedly acknowledged it, and there is no waiting period required between the contribution and the conversion. What to do: open both a traditional IRA and a Roth IRA at the same custodian, contribute, then convert — ideally within days, before the money earns much.

The Pro-Rata Rule — The Trap That Catches Everyone

This is the rule that turns a “tax-free” conversion into a taxable one. The pro-rata rule says that when you convert, the IRS treats all your traditional, SEP, and SIMPLE IRAs as one big pot. You cannot convert only your after-tax basis and leave the pre-tax money behind. Every dollar you convert is part basis and part taxable, in the same ratio as your total IRA balance, as explained by SmartAsset.

The math uses one fraction. Your nontaxable percentage equals your total after-tax basis divided by the total year-end value of all your traditional, SEP, and SIMPLE IRAs (plus the amount converted). The rest is taxable. The formula is:

[ \text{Taxable amount} = \text{Converted amount} \times \left(1 – \frac{\text{Total basis}}{\text{Total IRA value}}\right) ]

The consequence of ignoring this is a tax bill you did not expect. If you have a large pre-tax rollover IRA from an old 401(k), most of your “backdoor” conversion becomes taxable. A widespread misconception is that the IRA you contribute to is the only one that counts. It is not — the IRS aggregates every traditional, SEP, and SIMPLE IRA you own, across all custodians, measured on December 31 of the conversion year. What to do: before converting, check your combined IRA balances and decide whether you need to “isolate the basis” first (covered below).

Why a 401(k) Is the Escape Hatch

The pro-rata rule counts only IRAs — not 401(k)s, 403(b)s, or other workplace plans, per TIAA. That gives you a clean way out. If your employer plan accepts incoming rollovers, you can roll your pre-tax IRA money into the 401(k), which empties your traditional IRAs of pre-tax dollars.

After that rollover, the only money left in your IRAs is your after-tax basis. Now the pro-rata fraction is basically 100% basis, so your conversion is nearly tax-free. This move is called isolating the basis. The deadline that matters is December 31 of the conversion year — that is the snapshot date for IRA balances, so the rollover must clear before year-end, not by April. What to do: confirm your 401(k) accepts roll-ins, complete the pre-tax rollover by December 31, then convert the remaining basis.

Which Situation Applies to You?

The tax result depends entirely on what other IRA money you hold. Find your case below, then read the matching example.

You have no other traditional, SEP, or SIMPLE IRA. Your conversion is essentially tax-free. This is the clean backdoor Roth — read Sarah’s example.
You have a large pre-tax IRA (old 401(k) rollover). The pro-rata rule makes most of your conversion taxable unless you isolate the basis first — read David’s example.
You have old nondeductible basis sitting in a traditional IRA for years. Some of the conversion is tax-free, but earnings on that basis are taxable — read Maria’s example.
You are married. Each spouse’s IRAs are calculated separately; one spouse’s pre-tax IRA does not pollute the other’s conversion.
You are over age 59½. No early-withdrawal penalty applies, but the income tax on the taxable portion still does.

Worked Example 1 — The Clean Backdoor Roth

Sarah, age 38, earns $200,000 and is locked out of a direct Roth for 2025. She has no other traditional IRA money. She contributes $7,000 nondeductibly, then converts it a week later when it has grown by $20.

Total basis: $7,000.
Total IRA value at conversion: $7,020.
Nontaxable percentage: $7,000 ÷ $7,020 = 99.7%.
Taxable amount: only the $20 of earnings.

Sarah owes ordinary income tax on $20. At a 32% bracket, that is about $6 in tax. Her $7,000 basis moves to the Roth completely tax-free. This is the result the backdoor Roth is designed to deliver.

Worked Example 2 — Pro-Rata Bites Hard

David, age 45, has a $93,000 pre-tax rollover IRA from an old job. He contributes $7,000 nondeductibly and converts that $7,000, thinking it is tax-free.

Total basis: $7,000.
Total IRA value (all IRAs): $100,000.
Nontaxable percentage: $7,000 ÷ $100,000 = 7%.
Taxable amount: $7,000 × 93% = $6,510.

David expected a tax-free move but owes tax on $6,510. At a 32% bracket, that is about $2,083 in unexpected tax. Worse, his remaining basis stays trapped in the pre-tax IRA. Had David first rolled the $93,000 into his current 401(k) before December 31, only the $7,000 basis would remain, and his conversion would have been nearly tax-free. The fix existed; the timing killed it.

Worked Example 3 — Old Basis With Years of Growth

Maria, age 61, made $15,000 of nondeductible contributions over the years that grew to $25,000. She has no other IRAs and converts the whole $25,000 in 2025.

Total basis: $15,000.
Total IRA value: $25,000.
Nontaxable percentage: $15,000 ÷ $25,000 = 60%.
Taxable amount: $25,000 × 40% = $10,000.

Maria pays ordinary income tax on the $10,000 of growth; her $15,000 basis converts tax-free. Because she is over 59½, no 10% penalty applies. The lesson: basis converts free, but the earnings on that basis are always taxable on conversion.

How These Scenarios Play Out

If your IRA situation is…	Then your conversion tax result is…
Only nondeductible basis, no pre-tax IRAs	Nearly tax-free; you owe tax only on small earnings before conversion
Large pre-tax IRA alongside the new basis	Mostly taxable under pro-rata, unless you roll pre-tax money into a 401(k) by December 31
Old nondeductible basis with years of growth	Basis is tax-free; the accumulated earnings are taxed as ordinary income

When you do the conversion…	What happens to your tax bill…
Convert immediately after contributing	Almost no earnings accrue, so almost nothing is taxable
Wait months and let it grow first	The growth becomes taxable on conversion
Convert in a low-income year (job loss, gap year)	Same dollars taxed, but at a lower bracket — strategically smart

Where you forget the pro-rata snapshot…	The consequence you face…
You roll pre-tax money out in January after a December conversion	Too late — the December 31 balance already triggered pro-rata tax
You hold IRAs at two custodians and count only one	The IRS still aggregates both, raising your taxable amount
You skip Form 8606 entirely	The IRS treats the whole conversion as taxable, double-taxing your basis

Reporting It on Form 8606 — Line by Line

Every nondeductible contribution and every conversion goes on Form 8606, Nondeductible IRAs. You file it with your Form 1040 for the tax year, by the April deadline (April 15, 2026, for tax year 2025). If you and your spouse both do conversions, you each file a separate 8606.

Part I captures your basis. Line 1 is your nondeductible contribution for the year — for tax year 2025 you can make a 2025 contribution as late as April 15, 2026, and still count it, per WealthKeel’s guide. Line 2 is your prior-year basis from past 8606s. Line 6 is the total value of all your traditional, SEP, and SIMPLE IRAs on December 31 — this is the line that activates the pro-rata math.

Part II handles the conversion. Line 16 is the amount you converted, usually taken from the Form 1099-R your custodian sends. Line 17 is the basis applied to that conversion. Line 18 is line 16 minus line 17 — the taxable amount that flows to Form 1040, line 4b.

The consequence of filing it wrong is steep: a missing or incorrect 8606 lets the IRS tax your basis again, and there is a $50 penalty for failing to file the form when required. A common misconception is that tax software fills this in automatically — it often does not unless you answer the conversion questions correctly. What to do: enter the contribution and the conversion in separate steps in your software, then check that line 4b of your 1040 shows only the truly taxable amount.

Deadlines, Costs, and Timing

The contribution deadline for a 2025 nondeductible contribution is April 15, 2026. The conversion, however, is tracked by calendar year — a conversion done in 2025 is taxed in 2025, and the IRA-balance snapshot is December 31, 2025. There is no deadline to convert; you can leave basis in a traditional IRA for years, as Maria did.

Cost is usually low. Most custodians charge nothing to convert. Doing it yourself is free; the only “cost” is the income tax on the taxable portion. If you have a large pre-tax IRA, a multi-year conversion plan, or a messy basis history, hiring a CPA to model the tax — typically $300 to $800 for a focused projection — can save far more than it costs. This article is educational, not advice for your specific situation; when pro-rata, big balances, or estate questions are involved, talk to a CPA or tax attorney.

State Tax — Federal Is Only Half the Story

The federal rule is clear: only the pre-tax portion of a conversion is taxable. But your state may treat it differently, and you must check separately. Most states that have an income tax follow the federal treatment and tax the same taxable portion as ordinary income in the conversion year.

States with no income tax — such as Florida, Texas, Nevada, Washington, Wyoming, South Dakota, Alaska, Tennessee, and New Hampshire — do not tax the conversion at all, which is a genuine advantage of converting while living there. The consequence of guessing is mismatched returns: if you assume your state mirrors the federal taxable amount but it does not, your state return will be wrong. What to do: check your state’s department of revenue page for IRA conversion treatment, and if you are planning a move, consider timing a large conversion for a no-tax-state year.

Mistakes to Avoid

Forgetting old pre-tax IRAs. They trigger pro-rata tax on what you thought was a tax-free conversion.
Counting only one IRA. The IRS aggregates every traditional, SEP, and SIMPLE IRA — leaving one out understates your tax.
Rolling pre-tax money out in January. The December 31 snapshot already locked in pro-rata; the fix had to clear by year-end.
Skipping Form 8606. Without it, the IRS taxes your basis a second time and may add a $50 penalty.
Letting the contribution grow before converting. Every dollar of growth becomes taxable income at conversion.
Deducting the contribution by accident. If you deduct it, it is no longer basis, and the whole conversion becomes taxable.
Assuming your state follows federal rules. Some states tax conversions differently, producing a wrong state return.
Both spouses filing one 8606. Each spouse must file their own; combining them misreports basis.

Do’s and Don’ts

Do convert quickly after contributing, so little or no earnings accrue and stay taxable.
Do roll pre-tax IRA money into a 401(k) before December 31 to isolate your basis and avoid pro-rata tax.
Do file Form 8606 every year you have nondeductible activity, because the IRS will not track your basis for you.
Do keep copies of every 8606 permanently, since you may need decades of basis history at withdrawal.
Do check your state’s treatment, because federal tax-free does not always mean state tax-free.
Don’t assume only the IRA you funded counts — all IRAs are aggregated.
Don’t deduct a contribution you plan to convert; doing so erases your basis and makes it fully taxable.
Don’t convert in your highest-income year if you can wait for a lower-bracket year.
Don’t rely on software to auto-report the conversion without checking line 4b of your 1040.
Don’t forget that earnings on old basis are always taxable, even when the basis itself is not.

Pros and Cons of Converting

Pro — Tax-free growth. Once in the Roth, all future earnings come out tax-free in retirement, because you have already paid the tax.
Pro — No required minimum distributions. Roth IRAs have no RMDs during your lifetime, unlike traditional IRAs, per Investopedia.
Pro — Access for high earners. The backdoor route is the only way many high earners can fund a Roth at all.
Pro — Tax diversification. Roth money gives you a tax-free bucket to draw from, smoothing your retirement brackets.
Pro — Estate benefit. Heirs inherit Roth dollars income-tax-free, a strong wealth-transfer tool.
Con — Pro-rata tax. Existing pre-tax IRAs can make a large share of the conversion taxable now.
Con — Up-front tax cost. You pay tax this year on the taxable portion, reducing cash today.
Con — Five-year clock. Each conversion starts its own five-year rule for penalty-free access before 59½.
Con — Bracket risk. A large conversion can push you into a higher bracket or raise Medicare premiums.
Con — Complexity. Tracking basis and pro-rata math across years takes discipline and accurate forms.

The Five-Year Rule and No RMDs

Each Roth conversion carries its own five-year clock. If you are under 59½ and withdraw converted amounts within five years, you may owe a 10% penalty on the portion that was taxable, even though you already paid income tax on the conversion. The clock starts January 1 of the conversion year.

The consequence of ignoring it is a penalty on money you thought was free to use. A common misconception is that the Roth’s general five-year rule for earnings is the same as the conversion five-year rule — they are separate clocks. What to do: if you are under 59½, leave converted dollars untouched for five years, and label each conversion year so you know when each clock expires. Note also that Roth IRAs never require RMDs during your lifetime, so converted money can keep growing tax-free indefinitely.

What to Do Next

Add up every traditional, SEP, and SIMPLE IRA you own across all custodians — this tells you whether pro-rata will bite.
If you hold pre-tax IRA money, ask your 401(k) plan whether it accepts roll-ins, and complete that rollover before December 31 to isolate your basis.
Make the nondeductible contribution ($7,000 for 2025, $7,500 for 2026; add $1,000 if 50 or older) and convert it promptly.
File Form 8606 with your 1040 for the year, and confirm line 4b shows only the taxable portion.
Check your state’s rule on conversion income, and keep every 8606 copy permanently.
Call a CPA if you have large pre-tax balances, a multi-year conversion plan, or messy basis history.

FAQs

Can you convert a nondeductible IRA to a Roth if you earn too much? Yes. There is no income limit on Roth conversions for 2025 or 2026. The income limits apply only to direct Roth contributions, which is why high earners use the backdoor conversion route instead.

Do you pay taxes converting a nondeductible IRA to a Roth? Only on the pre-tax portion. Your after-tax basis converts tax-free, but any earnings and any pre-tax IRA money are taxed as ordinary income in the conversion year under the pro-rata rule.

What is the pro-rata rule? A formula that blends your IRAs. It treats all your traditional, SEP, and SIMPLE IRAs as one pot, so each converted dollar is part tax-free basis and part taxable, based on your December 31 balances.

Does a 401(k) count in the pro-rata calculation? No. Only IRAs count. Rolling pre-tax IRA money into a 401(k) before December 31 removes it from the calculation, letting you convert your basis nearly tax-free.

What form reports a nondeductible IRA conversion? Form 8606. You file it with your Form 1040 for the tax year, reporting both your nondeductible contribution in Part I and your conversion in Part II.

How much can I contribute for 2025 and 2026? $7,000 for 2025; $7,500 for 2026. Add $1,000 if you are age 50 or older, making the catch-up totals $8,000 for 2025 and $8,600 for 2026, per the IRS.

Is the backdoor Roth legal? Yes. The IRS recognizes the strategy, and there is no required waiting period between the contribution and conversion. You simply must report it correctly on Form 8606.

What happens if I never filed Form 8606? You risk double tax. Without it, the IRS has no record of your basis and may tax it again. You can file late or amended 8606s, but a $50 penalty may apply.

Does my state tax a Roth conversion? Usually, if it has an income tax. Most income-tax states tax the same taxable portion as the IRS. No-income-tax states like Florida and Texas do not tax conversions at all.

Can I undo a Roth conversion? No. Recharacterizing a conversion was eliminated by the 2017 tax law. Once you convert, the move is permanent, so confirm the tax cost before you act.

Do I owe a penalty if I’m under 59½? Not on the conversion itself. But each conversion starts a five-year clock; withdrawing the converted amount within five years before 59½ can trigger a 10% penalty.

Are there required minimum distributions on a Roth IRA? No. Roth IRAs have no RMDs during the owner’s lifetime, so converted funds can keep growing tax-free for as long as you live.

This article reflects federal rules as of June 2026 and covers tax years 2025 and 2026. Tax law changes — confirm current figures with the IRS or a licensed professional before you file. Word count: approximately 3,650.

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