The deadline to set up a SEP IRA for a given tax year is the due date of your business’s federal income tax return for that year, including extensions. File an extension and you get the extended due date, even if you send the return in earlier. That timing is what makes the SEP IRA unusual: you can establish the plan and fund it months after the tax year has already closed, once you know exactly what your income looked like.1Internal Revenue Service. Retirement Plans FAQs Regarding SEPs
Deadlines by Business Type
The exact date depends on which return your business files. All of the dates below assume a calendar-year filer; a fiscal-year business uses the corresponding due date for its own return. When a deadline falls on a weekend or federal holiday, it shifts to the next business day.
- Sole proprietors filing Schedule C: April 15 without an extension, October 15 with a six-month extension filed on Form 4868.
- Partnerships (Form 1065) and S corporations (Form 1120-S): March 15 without an extension, September 15 with a six-month extension filed on Form 7004.2Internal Revenue Service. Starting or Ending a Business
- C corporations (Form 1120): April 15 without an extension, October 15 with a six-month extension filed on Form 7004.2Internal Revenue Service. Starting or Ending a Business
Filing the extension is what buys you the extra months. Once you file the extension form for your business return, both the establishment and funding deadlines move to the extended due date automatically.1Internal Revenue Service. Retirement Plans FAQs Regarding SEPs
Why This Matters If You’re Starting from Scratch
The generous back-dated deadline is the main reason people reach for a SEP IRA after the year is over. A solo 401(k), by contrast, has to be established by December 31 of the tax year you want to contribute for. The plan documents have to be signed before the year closes, even if the money goes in later.
A SEP IRA has no such requirement. You can create the plan and fund it in the same afternoon, months into the following year. If it’s already January or February and you have no retirement plan in place for the year that just ended, the SEP IRA is likely your only route to a deductible employer contribution for that year.
What You Have to Do Before the Deadline
“Setting up” a SEP IRA is not one step. Three things have to be finished before you deposit any contribution for the prior tax year:
- Adopt a written plan agreement.
- Open a SEP IRA account for every eligible employee, including yourself.
- Give each eligible employee written notice of the plan.
Adopt the Written Agreement
Most small business owners use the IRS model form, Form 5305-SEP. You fill it out and sign it, but you do not file it with the IRS. Keep it in your permanent business records.3Internal Revenue Service. Form 5305-SEP
One boundary to know: if your business also sponsors another qualified retirement plan such as a 401(k), you cannot use Form 5305-SEP. You’ll need a prototype or individually designed SEP agreement instead.1Internal Revenue Service. Retirement Plans FAQs Regarding SEPs
Open the Accounts
Every eligible employee needs their own SEP IRA account at a financial institution. Under the default rules, an employee is eligible if they are at least 21 years old, have worked for you in at least three of the last five years, and received at least $800 in compensation during 2026.4Internal Revenue Service. 2026 Amounts Relating to Retirement Plans and IRAs You are free to use looser eligibility rules, but not stricter ones.5Internal Revenue Service. Simplified Employee Pension Plan (SEP)
Notify Employees
Before you fund the plan, give each eligible employee a copy of the completed Form 5305-SEP along with a statement explaining how contributions work and the rules for participation.3Internal Revenue Service. Form 5305-SEP
All three steps have to be complete before the money hits the account, and all three have to be done by your return’s due date, including extensions, to count for the prior tax year.
The Practical Timeline
If you’re a sole proprietor doing this in April, the sequence usually looks like this. Decide on your contribution amount based on the year’s net profit. Complete and sign Form 5305-SEP. Open a SEP IRA at your chosen custodian. If you have employees, deliver their notices and open their accounts. Then deposit the contribution and tell the custodian which tax year it applies to. The last piece matters, because a contribution made between January 1 and the deadline can count for either the prior year or the current year, and the custodian codes it based on what you tell them.
If the return itself isn’t ready by the original due date, file the extension. That single step preserves your SEP window through October (or September for partnerships and S corporations) and gives you time to finalize the numbers before depositing anything.
If You Miss the Deadline
Once your extended filing deadline passes, the window is closed. You cannot go back and make a SEP IRA contribution for that prior tax year. There is no late-filing workaround.
What you can do is set up the plan now for the current tax year. A SEP IRA does not have to be established at the start of the year. You can create it in July and still make a full contribution for the current tax year, provided you fund it by that year’s return deadline. The contribution limits are the same whether you set the plan up in January or in October.
If you’re a sole proprietor with no employees and you missed the SEP window for last year, check whether a traditional or Roth IRA contribution for that year is still open to you. Those contributions have a firm April 15 deadline that extensions do not move, and the dollar limits are much lower than a SEP, but the option is there when the SEP option is not.