If you filed a tax extension back in April, you likely still have time to make a SEP-IRA contribution for the 2025 tax year. The deadline for that contribution matches your extended return’s due date, October 15, 2026 — not the original April 15 deadline you might assume already passed. This is one of the only retirement accounts where filing an extension genuinely buys you extra time to contribute, not just extra time to file paperwork. The catch: the limits that apply are 2025’s, not 2026’s, and getting that distinction wrong can mean overcontributing.
The Short Answer
A SEP-IRA contribution for a given tax year is due by your tax filing deadline for that year, including any extension you filed. For most sole proprietors and single-member LLC owners, October 15, 2026 is the last day to make a SEP-IRA contribution counted toward the 2025 tax year — as long as you filed Form 4868 by the original April 15 deadline. This applies whether you’ve already filed your 2025 return or haven’t filed it yet. The IRS confirms the contribution deadline runs to the end of your extension period regardless of when you actually submit the return itself.
Why SEP-IRAs Work Differently Than Other Retirement Accounts
Traditional and Roth IRA contributions for a given tax year have to be made by the original filing deadline, April 15, with no extension available no matter what paperwork you filed. A SEP-IRA follows a different rule entirely, because it’s structured as an employer plan rather than an individual account. Establishing and funding a SEP-IRA ties to your business’s tax return due date, extensions included. The IRS states this directly: obtain a valid extension for filing your return, and you have until the end of that extension period to deposit the contribution, regardless of when you actually file. That’s a real, structural difference, not a workaround or a loophole. It’s the reason this deadline matters specifically for self-employed people who extended.
Does This Apply to Everyone Who Extended?
The October 15, 2026 date applies to sole proprietors, single-member LLCs, and C corporations that filed a valid extension for their 2025 return. If your business files as a partnership or an S corporation, your original deadline was March 15. An extension pushes your SEP deadline to September 15, 2026 instead — a full month earlier. Most freelancers and independent contractors filing Schedule C as individuals fall into the October 15 group. It’s still worth confirming which category actually applies to you before assuming the later date.
If you never filed an extension at all, this window already closed on your original filing deadline. There’s no way to reopen it retroactively just by deciding now that you want to contribute more for 2025.
How Much Can You Actually Contribute for 2025?
This is where the tax-year distinction matters most. This contribution counts toward 2025, so the applicable limits are 2025’s — not the higher figures that apply starting with 2026 income. For the 2025 tax year, a SEP-IRA contribution caps at the lesser of 25% of compensation or $70,000, with compensation itself capped at $350,000 for this purpose.
For a self-employed individual filing Schedule C, “compensation” isn’t simply your net profit. It’s net earnings from self-employment, reduced by the deductible half of your self-employment tax. That two-step calculation effectively works out to about 20% of adjusted net profit, rather than a straightforward 25%. EarnerLedger’s Solo 401(k) vs SEP IRA comparison covers this mechanic in more depth, including how it stacks up against a Solo 401(k)’s different contribution structure.
A Worked Example
Say a freelance consultant had $95,000 in net Schedule C profit for the 2025 tax year. They filed a valid extension in April, and are now deciding how much to contribute to a SEP-IRA before October 15.
| Step | Amount |
|---|---|
| 2025 net Schedule C profit | $95,000 |
| Net earnings from self-employment (92.35% of profit) | $87,732.50 |
| Self-employment tax (15.3% of that figure) | $13,423.07 |
| Deductible half of self-employment tax | $6,711.54 |
| Adjusted net earnings ($95,000 − $6,711.54) | $88,288.46 |
| Maximum SEP-IRA contribution (20% of adjusted net earnings) | $17,657.69 |
That figure sits comfortably under the 2025 cap of $70,000, so the 25%-of-compensation calculation — expressed here as the equivalent 20% of adjusted net earnings — is what actually limits the contribution, not the flat dollar cap. This is a simplified illustration; a tax professional can confirm the exact figure based on your complete return.
What If You Haven’t Filed Your 2025 Return Yet?
You can still make the SEP-IRA contribution before October 15 even if your return itself isn’t filed yet, as long as your extension was valid and timely. The contribution deadline runs to the end of the extension period regardless of when the actual return gets submitted. That said, waiting until the very last days of the extension window leaves little room for error. Your accountant may need to recalculate your exact contribution limit based on final numbers, and a last-minute rush doesn’t leave time to fix a mistake.
Does This Affect Your Solo 401(k) Too?
No — and this is a common point of confusion worth clearing up directly. A Solo 401(k) employee deferral for a given tax year has to be made by December 31 of that year, with no extension available, regardless of when you file your return. The employer contribution portion of a Solo 401(k) does follow the same extended-deadline rule as a SEP-IRA. But if you’re hoping to still make an employee deferral for 2025 specifically, that window closed on December 31, 2025 — filing an extension for your return doesn’t reopen it. EarnerLedger’s guide to Solo 401(k) contribution limits breaks down the full employee/employer structure in detail.
Common Mistakes
- Using 2026 contribution limits instead of 2025’s. A contribution made now, in September or October 2026, for the 2025 tax year follows 2025’s $70,000 cap and $350,000 compensation limit — not the higher 2026 figures.
- Assuming the extension deadline applies to every retirement account. It doesn’t extend traditional or Roth IRA contribution deadlines. It doesn’t reopen a missed Solo 401(k) employee deferral window either.
- Confusing the partnership/S-corp deadline with the sole proprietor deadline. The former lands a full month earlier, on September 15.
- Waiting until October 14 to calculate the exact contribution amount. The calculation depends on final net profit figures. Leaving no buffer for last-minute corrections is a real risk.
- Assuming you can still contribute if you never filed an extension. Without a valid extension on file, the deadline was your original filing date, with no later option.
Frequently Asked Questions
Can I still make a SEP-IRA contribution for 2025 if I already filed my return? Yes, as long as you filed a valid extension in April, even if you later filed your actual return before October 15. The deadline runs to the end of the extension period regardless of when you filed.
What’s the SEP-IRA contribution limit for the 2025 tax year specifically? The lesser of 25% of compensation or $70,000, with compensation capped at $350,000. That’s different from the 2026 figures of $72,000 and $360,000, which apply to a different tax year.
Does the October 15 deadline apply to everyone who’s self-employed? It applies to sole proprietors, single-member LLCs, and C corporations that filed a valid extension. Partnerships and S corporations that extended have an earlier SEP deadline of September 15.
Does this also extend my Solo 401(k) employee deferral deadline? No. A Solo 401(k) employee deferral for 2025 had to be made by December 31, 2025, regardless of any extension. Only the employer contribution portion follows the extended deadline.
What if I never filed an extension for my 2025 return? Then your SEP-IRA contribution deadline for 2025 was your original filing deadline. That window has already closed with no way to reopen it now.
Bottom Line
If you extended your 2025 tax return, October 15, 2026 isn’t just your filing deadline. It’s also your last opportunity to fund a SEP-IRA for that tax year, using 2025’s contribution limits rather than 2026’s. The math is straightforward once you know the right starting numbers: roughly 20% of your adjusted net self-employment earnings, capped at $70,000 for 2025. Confirming the exact figure with a tax professional before the deadline is worth the effort, especially if your final numbers shifted after you filed the extension back in April.
This article is for general educational purposes and reflects federal tax guidance in effect for the 2025 and 2026 tax years at the time of writing. It is not individualized tax advice. Consult a CPA, enrolled agent, or other qualified tax professional for guidance specific to your situation.
Official Sources
- IRS — Retirement Plans FAQs Regarding SEPs (irs.gov/retirement-plans/retirement-plans-faqs-regarding-seps) — confirms the extended contribution deadline runs to the end of a valid extension period regardless of when the return is filed
- IRS — Publication 560, Retirement Plans for Small Business — SEP contribution and deadline rules, including the entity-specific due dates
- IRS — 2025 SEP-IRA contribution limit ($70,000 / $350,000 compensation cap) and 2026 limits ($72,000 / $360,000), per annual cost-of-living adjustment guidance
- IRS — Self-employment tax (Social Security and Medicare taxes) — the 92.35%/15.3% mechanic used to calculate adjusted net earnings