For most people the answer is no. The last day to open a SEP IRA and fund it for 2025 was the due date of the 2025 return, including extensions: April 15, 2026, or October 15, 2026 if you filed the standard extension. Both dates have passed. A deposit you make now counts toward 2026, so ask your custodian to record it that way.
The one possible exception is a deadline postponed after a federally declared disaster, covered further down. The rest of this guide explains the rule behind the date, the deadlines for 2026, what a Solo 401(k) allows for 2026, the 2025 limits for reference and how to make sure each deposit is recorded in the right year.
Why the deadline was October 15, and what it means now
The IRS gives you until October 15 to file if you ask for the extension by the April due date. It also says plainly that the extension is only for filing your return, so any tax you owe was still due in April (IRS).
For a SEP, what matters is the due date of your return including extensions. The IRS SEP FAQ says you can set up a SEP for a year as late as that date. It also says you must deposit the contributions by then, and that with an extension you have until the end of the extension period to deposit, whatever date you file the return (IRS SEP FAQs). Publication 560 says the same (Publication 560).
Two consequences for 2025:
- With an extension, the date was October 15, 2026, whether you filed your return in June or in October.
- Without an extension, the date was April 15, 2026. The IRS FAQ adds that if you did not request an extension and did not deposit the SEP contributions by the filing due date, you are not allowed to deduct them on that year’s return.
Nothing in the IRS sources we checked lets a deposit made after the due date count for that earlier year. If you missed it, a deposit now is still useful, but it belongs to 2026.
Deadlines by tax year
| Tax year | Return due | With an extension | Status in October 2026 |
|---|---|---|---|
| 2025 | April 15, 2026 | October 15, 2026 | Closed |
| 2026 | April 15, 2027 | October 15, 2027 | Open |
2025
- Return due
- April 15, 2026
- With an extension
- October 15, 2026
- Status in October 2026
- Closed
2026
- Return due
- April 15, 2027
- With an extension
- October 15, 2027
- Status in October 2026
- Open
Opening the SEP and making the contribution are both tied to the due date of your return for that year, including extensions (Publication 560). The dates are the ordinary April 15 and October 15 return dates. A disaster postponement can move them.
What you can still do for 2026
SEP IRA. You can open one for 2026 at any point up to the due date of your 2026 return, including extensions, and you deduct the contribution if you deposit it by that same date. Our SEP IRA guide explains how the plan works and who it suits. If you already have a Solo 401(k), a SEP does not give you a second pile of room, because contributions to both are added together against the same annual limit. The guide to using a SEP IRA and a 401(k) together covers it.
Solo 401(k). The plan has two pieces, and the deadlines differ.
| Piece | Deadline | Condition |
|---|---|---|
| Employee deferral, plan in place | Elect by December 31, 2026; deposit by the return due date, including extensions | Publication 560: owner-employees must elect deferrals by the end of the tax year |
| Employee deferral, new plan adopted after year-end | April 15, 2027, with no extension | Only for a sole owner of an unincorporated business who is its only employee, for the first year only (SECURE 2.0, section 317) |
| Employer contribution | Return due date, including extensions (October 15, 2027 with an extension) | New or existing plan |
Employee deferral, plan in place
- Deadline
- Elect by December 31, 2026; deposit by the return due date, including extensions
- Condition
- Publication 560: owner-employees must elect deferrals by the end of the tax year
Employee deferral, new plan adopted after year-end
- Deadline
- April 15, 2027, with no extension
- Condition
- Only for a sole owner of an unincorporated business who is its only employee, for the first year only (SECURE 2.0, section 317)
Employer contribution
- Deadline
- Return due date, including extensions (October 15, 2027 with an extension)
- Condition
- New or existing plan
Sources: IRS Publication 560 (2025), Table 1 and the definition of elective deferrals; IRS issue snapshot on contributions to a 401(k) plan made after the end of the tax year (IRC 401(b)(2) as amended by SECURE Act section 201 and SECURE 2.0 section 317).
The IRS issue snapshot says a plan must exist before compensation can be deferred and that “retroactive elective deferrals are not generally permitted.” The sole-owner exception is the narrow way around that rule. Its wording covers an “unincorporated business”, so it does not fit an S corporation. The simpler route, if you want a 2026 employee deferral, is to open the plan before December 31, 2026. Our step-by-step guide to opening a Solo 401(k) walks through the paperwork.
The 2026 limits. The SEP and total plan cap is $72,000 for 2026 (the smaller of that or 25% of compensation for a SEP), and the employee deferral is $24,500 (IRS Notice 2025-67 and IR-2025-111). To test your own profit level, use the retirement contribution calculator, which uses the 2026 limits.
Make sure each deposit lands in the right year
Your custodian may record a deposit as the current year’s contribution unless you say otherwise. Before you send money:
- Tell the custodian the tax year. Look for a “tax year” or “prior year” field when you fund the account, or ask support to confirm. If the form has no such field, contact them before depositing.
- Use a SEP or plan deposit, not a regular IRA contribution. A SEP contribution is an employer contribution, so it should not be coded against your personal IRA limit.
- Keep the confirmation. Save the receipt or statement showing the amount, the date and the year it is assigned to. Your tax preparer will want it.
- Check the statement a few weeks later. If a deposit you made for 2025 before October 15 shows as 2026, ask the custodian to correct it before you file.
If you did fund a SEP for 2025 in time, the contribution is deducted on line 16 of Schedule 1 (Form 1040) of your 2025 return for sole proprietors and partners (Publication 560). It lowers income tax, but not self-employment tax, which is still figured on your full profit.
The 2025 limits, for reference
These are the 2025 figures. They apply to a 2025 deduction and should not be mixed with the 2026 numbers above.
| Item | 2025 |
|---|---|
| SEP IRA: smaller of this or 25% of compensation | $70,000 |
| Solo 401(k) employee deferral | $23,500 |
| Catch-up if age 50 or over (not 60 to 63) | +$7,500 |
| Catch-up if age 60, 61, 62 or 63 | +$11,250 |
| Total annual additions to a plan, before catch-up | $70,000 |
| Maximum compensation counted for the plan | $350,000 |
SEP IRA: smaller of this or 25% of compensation
- 2025
- $70,000
Solo 401(k) employee deferral
- 2025
- $23,500
Catch-up if age 50 or over (not 60 to 63)
- 2025
- +$7,500
Catch-up if age 60, 61, 62 or 63
- 2025
- +$11,250
Total annual additions to a plan, before catch-up
- 2025
- $70,000
Maximum compensation counted for the plan
- 2025
- $350,000
Sources: IRS, 401(k) limit increases to $23,500 for 2025 (deferral and catch-ups); IRS Publication 560 (2025), Table 1 ($70,000 and $350,000).
For a self-employed person, “25% of compensation” works out to about 20% of net profit after subtracting half of your self-employment tax. The IRS explains why on its page about calculating your own contribution: your compensation is reduced by the contribution itself.
Example: a hypothetical freelancer with $80,000 of net profit in 2025
Take a hypothetical freelancer under 50 with no employees and no other retirement plan, whose Schedule C net profit for 2025 was $80,000. We ran the case through the same retirement calculator code the site uses, with the 2025 limits.
| Step | Amount |
|---|---|
| Net earnings from self-employment ($80,000 × 92.35%) | $73,880 |
| Self-employment tax (15.3%) | $11,304 |
| Deductible half of SE tax | $5,652 |
| Compensation for the plan ($80,000 − $5,652) | $74,348 |
| SEP IRA or employer contribution (20% of $74,348) | $14,870 |
| Plus employee deferral, only in a plan that existed and had the election made before Dec 31, 2025 | $23,500 |
| Solo 401(k) total with the deferral (existing plan only) | $38,370 |
Net earnings from self-employment ($80,000 × 92.35%)
- Amount
- $73,880
Self-employment tax (15.3%)
- Amount
- $11,304
Deductible half of SE tax
- Amount
- $5,652
Compensation for the plan ($80,000 − $5,652)
- Amount
- $74,348
SEP IRA or employer contribution (20% of $74,348)
- Amount
- $14,870
Plus employee deferral, only in a plan that existed and had the election made before Dec 31, 2025
- Amount
- $23,500
Solo 401(k) total with the deferral (existing plan only)
- Amount
- $38,370
Computed with the site's retirement contribution calculator using 2025 limits. Amounts are maximums, rounded to the nearest dollar.
In practice, someone with no plan in place could have put in about $14,870 for 2025, whether through a SEP or a newly adopted Solo 401(k), because a new plan had no 2025 deferral. The $38,370 total applied only to a plan that already existed with the $23,500 deferral elected before December 31, 2025. A SEP has no required amount, so putting in less was always allowed.
If a disaster postponed your deadlines
The IRS postpones filing and payment deadlines for people in federally declared disaster areas. If your county is on the list, your 2025 due date may be later than October 15, 2026, and the retirement contribution deadline follows your return’s due date. The IRS keeps the current list on its disaster relief page. Read the notice for your disaster before counting on a later date, since each notice spells out what it covers.
What to do now
- You funded a plan for 2025 before the deadline: keep the confirmation showing the year and amount, and give it to your tax preparer.
- You missed the 2025 date: plan for 2026. A SEP can be opened and funded up to the 2026 return due date, including extensions.
- You want a 2026 employee deferral in a Solo 401(k): open the plan and elect the deferral before December 31, 2026.
- You are comparing plans: the Solo 401(k) vs. SEP IRA comparison shows which one allows more at each income level.
