You can do a Backdoor Roth IRA with a SEP IRA, but not while the SEP still holds pre-tax money. The IRS aggregates every non-Roth IRA you own when it calculates the tax on a Roth conversion, so a funded SEP turns what should be a tax-free conversion into a mostly taxable one. The workable path is to roll your SEP balance into a 401(k) or Solo 401(k) first, confirm the SEP is empty, and only then make your non-deductible contribution and convert.
Why the SEP IRA Breaks the Strategy
A SEP IRA is funded entirely with pre-tax employer contributions. For a self-employed person who has been contributing for years, the balance can easily run into six figures, and none of those dollars has ever been taxed.
Under the IRA aggregation rule in Internal Revenue Code Section 408, when you convert any IRA to a Roth, the IRS treats all of your non-Roth IRAs as a single combined account for tax purposes.1Office of the Law Revision Counsel. 26 USC 408 Individual Retirement Accounts Traditional IRAs, rollover IRAs, SIMPLE IRAs, and SEP IRAs all go in the pool. It makes no difference that you’re converting only the small Traditional IRA you just funded with after-tax dollars. The agency looks at the total balance across every non-Roth IRA you own.
That total feeds the pro-rata rule. You divide your after-tax basis (your non-deductible contribution) by the combined value of all your non-Roth IRAs as of December 31 of the conversion year.1Office of the Law Revision Counsel. 26 USC 408 Individual Retirement Accounts The resulting percentage is the tax-free share of your conversion. Everything else is ordinary income.
What the Tax Actually Looks Like
Suppose you have $100,000 in a SEP IRA and you make a $7,500 non-deductible contribution to a new Traditional IRA to convert.
Your total non-Roth IRA balance is $107,500. Your after-tax basis is $7,500. The tax-free portion is $7,500 divided by $107,500, roughly 7%. When you convert the $7,500, only about $523 escapes tax. The remaining $6,977 is added to your taxable income for the year. If you already sit in a high bracket, you’ve paid real tax to accomplish essentially nothing.
The larger the SEP, the worse it gets. At $250,000 in a SEP, the tax-free percentage drops below 3%. The Backdoor Roth only works cleanly when your non-Roth IRA balances are at or near zero on December 31 of the conversion year. A funded SEP makes that impossible without moving money out first.
The Fix: Roll the SEP Into a 401(k)
Employer-sponsored qualified plans are not counted in the IRA aggregation rule.1Office of the Law Revision Counsel. 26 USC 408 Individual Retirement Accounts The IRS rollover chart confirms that SEP IRA funds can move into a qualified plan.2Internal Revenue Service. Rollover Chart If your employer offers a 401(k) and the plan accepts inbound rollovers, you can transfer your SEP balance into it and clear your IRA slate.
Check with the plan administrator or read the summary plan description to confirm the plan accepts rollovers in. If it does, request a direct rollover (a trustee-to-trustee transfer) from your SEP IRA custodian to the 401(k). A direct rollover avoids the 20% mandatory withholding that applies when retirement plan distributions are paid to you personally.3Internal Revenue Service. Rollovers of Retirement Plan and IRA Distributions
Timing is everything. The rollover must settle and the SEP balance must reach zero before you convert. The pro-rata calculation uses your December 31 balance, so any pre-tax IRA dollars sitting in the account at year-end will contaminate the conversion. Small earnings that accrue in the SEP during the transfer window need to go into the rollover too. Once the SEP is empty, you make the non-deductible contribution and convert, and the formula becomes $7,500 over $7,500. The whole conversion is tax-free.
The Solo 401(k) Route for the Self-Employed
Most people with a SEP IRA are self-employed or run a small business with no employees other than a spouse. They don’t have an outside employer 401(k) to roll into. The answer is a Solo 401(k), sometimes called an individual 401(k).
A Solo 401(k) is a qualified retirement plan for self-employed individuals with no full-time employees (a working spouse is the exception). Because it’s a qualified plan, it sits outside the IRA aggregation calculation. Solo 401(k) plans can accept inbound rollovers from SEP IRAs when the plan document permits it, and since you control the plan, you can choose a provider whose document includes that provision.
The sequence looks like this:
- Open a Solo 401(k) with a provider whose plan document allows inbound IRA rollovers. Confirm this before you set the account up.
- Request a direct rollover from your SEP IRA custodian to the Solo 401(k), moving the entire balance including residual earnings.
- Wait for the transfer to settle and verify the SEP IRA shows a $0 balance.
- Make your non-deductible contribution to a Traditional IRA and designate it as non-deductible.
- Convert the Traditional IRA to a Roth IRA.
One trade-off: a Solo 401(k) carries slightly more paperwork than a SEP. Once plan assets exceed $250,000, you must file Form 5500-EZ annually with the Department of Labor. A SEP IRA has no filing requirement. For most people the tax-free conversion is worth the modest administrative burden, and you can direct future retirement contributions into the Solo 401(k), which generally has comparable or better contribution room than the SEP.
If You Can’t Roll the SEP Anywhere
If you have no employer plan and can’t establish a Solo 401(k) (for example, because you have full-time W-2 employees), your options narrow. You could convert the whole SEP to a Roth and pay tax on the entire pre-tax balance. For a large SEP that can mean a six-figure tax bill in a single year, possibly pushing you into the top marginal bracket.
Some people spread it out, converting portions of the SEP across several years to keep each year’s taxable amount within a bracket they’re willing to accept. That reduces the total cost but delays the Backdoor Roth, because any remaining pre-tax balance keeps triggering the pro-rata rule during the interim years. A self-employed person with common-law employees could also set up a full 401(k) plan covering those employees, which costs more and takes more work but opens the same escape hatch for the SEP money.
Your Spouse’s SEP Doesn’t Count
The aggregation rule applies to each spouse individually. If your spouse holds a SEP IRA or a Traditional IRA full of pre-tax money, it has no effect on your Backdoor Roth. There is no joint IRA, and the IRS does not aggregate accounts across spouses. Your conversion is calculated using only your own IRA balances. A couple where one spouse has a large SEP and the other has a clean IRA slate can execute the Backdoor Roth for the clean spouse right away, while they work on moving the other spouse’s SEP into a qualified plan.
Reporting the Conversion on Form 8606
Correct reporting is what keeps the IRS from taxing your conversion twice. File Form 8606 (Nondeductible IRAs) with your Form 1040 for any year you make a non-deductible contribution or convert IRA funds to a Roth.4Internal Revenue Service. About Form 8606, Nondeductible IRAs
Line 1 records your non-deductible contribution and establishes your after-tax basis.5Internal Revenue Service. Instructions for Form 8606 Part II handles the conversion, reconciling the basis against the amount converted to compute the taxable portion.
Your custodian will issue two forms: a Form 5498 reporting the contribution and a Form 1099-R reporting the conversion as a distribution.5Internal Revenue Service. Instructions for Form 8606 Expect the 1099-R to show the full converted amount in Box 2a and the “Taxable amount not determined” box checked in Box 2b.6Internal Revenue Service. Instructions for Forms 1099-R and 5498 The custodian doesn’t know your basis, so it reports the gross amount and leaves the actual tax figure to you. You calculate the taxable portion on Form 8606.
Skipping Form 8606 is expensive. If you fail to file it for the year of a non-deductible contribution, the IRS has no record of your basis and can treat the entire conversion as taxable. There is also a $50 penalty for not filing when required.7Internal Revenue Service. Instructions for Form 8606 The real cost is the lost basis tracking, which forces you to pay tax again on money that was already taxed.
Timing the Steps
A non-deductible Traditional IRA contribution for the 2026 tax year can be made anytime from January 1, 2026 through the federal tax filing deadline of April 15, 2027.8Internal Revenue Service. Retirement Topics – IRA Contribution Limits The conversion, though, counts in the calendar year it actually happens. Contribute in March 2027 for the 2026 tax year and convert in March 2027, and the conversion is a 2027 tax event measured against your December 31, 2027 IRA balances.
Keep the sequence inside one calendar year when you can. Roll the SEP into the employer plan early, confirm a zero balance, then contribute and convert. Waiting until late in the year invites processing delays that can leave pre-tax dollars in the IRA on December 31 and contaminate the whole conversion. Leave at least a few weeks between the rollover finishing and the conversion going through.