SEP IRA Contribution Deadline: The Complete Guide

The SEP IRA contribution deadline is the most misunderstood date in small business retirement planning, and the confusion is expensive in both directions. People assume it was December 31 and give up on a deduction they could still take. Other people assume it is April 15 for everybody, miss a March deadline they never knew applied to them, and lose the deduction they were counting on.

Neither is right. The deadline moves depending on how your business files, and for most people it is later than they think.

The Rule in One Sentence

Your SEP contribution is due on the due date of your business income tax return for that year, including extensions.

That is the whole rule, and every specific date below is just that sentence applied to a particular filing situation. There is no separate SEP calendar. The plan borrows the tax return's deadline, which is why the answer changes depending on what return you file, and why an extension on the return is an extension on the contribution.

You will see this date called a lot of different things, and they all mean the same deadline: the SEP IRA funding deadline, the SEP IRA deposit deadline, the SEP plan contribution deadline, the deadline for contributing to a SEP IRA. One date, many names. The sentence above is it.

Two things follow from it that catch people out. First, December 31 is irrelevant. The year has to close before you can even know your profit, and the rules are built around that. Second, April 15 is not a universal answer, because plenty of businesses do not file an April 15 return.

Your Exact Date by Entity Type

For a calendar-year business, these are the dates. Find your row and stop guessing.

Sole proprietor or single-member LLC, filing Schedule C with your Form 1040. Due April 15. With a valid extension, October 15.

Partnership or multi-member LLC, filing Form 1065. Due March 15. With a valid extension, September 15.

S corporation, filing Form 1120-S. Due March 15. With a valid extension, September 15.

C corporation, filing Form 1120. Due April 15. With a valid extension, October 15.

The pattern is worth internalizing rather than memorizing. Pass-through entities that issue K-1s file a month earlier, because their owners need those K-1s to finish their personal returns. So if you run an S corp and think of April 15 as your deadline because that is when your 1040 is due, you are a month late on the SEP without realizing it. The SEP follows the business return, not your personal one.

If your business does not use a calendar year, apply the same rule to your own fiscal year: the due date of that year's return, plus extensions.

How Extensions Move It

A valid extension moves the SEP deadline by the full six months, because the statute ties the deadline to the due date including extensions rather than to a fixed calendar date.

The extension has to be real and filed on time. Form 4868 for an individual return, Form 7004 for a business return. Filing the extension is what buys the time, not intending to file it, and not simply filing the return late.

This is the part worth planning around deliberately. Extending the return is a free option that buys six more months to fund the plan, which matters when the cash is not available in March or when you want your accountant to finish the numbers before you decide how much to put in. Plenty of business owners extend for exactly this reason and nothing else.

What does not work: filing late without an extension. If the return was due March 15 and you filed it in June with no extension on record, your SEP deadline was March 15. A contribution made in June is not deductible for that year, and it does not automatically become a contribution for the current year either.

The Setup Deadline Is the Same Deadline

People search separately for whether they can still set up a SEP for last year, and the answer surprises them: yes, and it is the same date.

The deadline to contribute to a SEP IRA and the deadline to open one are the same date. You can establish a SEP for a prior year as late as the due date of that year's business return, including extensions. Open the plan and fund it in the same sitting, in October, for a year that ended nine months earlier.

That is genuinely unusual. Most retirement plans require you to have made a decision before the year ended. The SEP lets you look backward at a finished, profitable year and create a deduction for it after the fact, with complete information about what you actually earned.

Practically, setting one up means adopting a plan document, which for most small businesses is IRS Form 5305-SEP, and then opening the SEP-IRA accounts to receive the money. Form 5305-SEP is kept in your records rather than filed with the IRS. If you have employees, or if you use a prototype document from a financial institution, the paperwork is more involved and worth starting earlier than the deadline.

Why This Beats a Solo 401(k) Looking Backward

When someone realizes in September that last year was more profitable than expected, the SEP is usually the only plan still fully available, and the reason is timing.

A Solo 401(k) has two moving parts: an employee elective deferral and an employer profit sharing contribution. The employer piece follows roughly the same extended deadline logic a SEP does. The employee deferral is the problem. Deferrals are salary reductions, and a salary reduction has to be elected before the compensation is earned, which for most people means a decision made during the year rather than after it. There is a narrow SECURE 2.0 provision that gives sole proprietors adopting a brand new solo plan some room to make first-year deferrals after year end, and it is genuinely narrow. Do not assume it covers you without checking the specifics with your preparer.

A SEP has none of that structure. The entire contribution is an employer contribution, decided and made after the year closes. There is no deferral election to have missed.

The trade is real, though, and it goes the other way during the year. A Solo 401(k) generally lets a lower-income self-employed person put away more, because the deferral is a flat dollar amount rather than a percentage of profit, and because it allows catch-up contributions at 50 and older. A SEP has no catch-up at all. If you are planning forward rather than looking backward, compare them properly using the SEP versus Solo 401(k) comparison and the plan selector.

The SEP Deadline vs the IRA Deadline

These are two different deadlines with two different rules, and conflating them costs people real money every year.

A personal IRA contribution, Traditional or Roth, is due April 15. Extensions do not move it. Filing an extension on your return buys you nothing on your personal IRA.

A SEP contribution is due with the business return and extensions do move it.

So an extended sole proprietor sitting in July has missed the personal IRA window entirely and still has three months of SEP room. Someone who assumed the two dates worked the same way just lost a deduction they did not have to lose.

Worth knowing in the other direction too: these are separate limits, not one shared pool. A SEP contribution is an employer contribution and does not consume your personal IRA contribution room. You can take a SEP contribution and still make your own IRA contribution for the same year. Being covered by the SEP does affect whether the Traditional IRA piece is deductible, which is a different question from whether you are allowed to make it.

How Much You Can Actually Contribute

For 2026, a SEP contribution is limited to the lesser of 25% of compensation or $72,000. The compensation used in that calculation is itself capped at $360,000 under section 401(a)(17).

If you are an employee of your own corporation, that 25% runs against your W-2 wages and the math is straightforward.

If you are self-employed and contributing on your own net earnings, the 25% is not what you actually get. Your contribution reduces your net earnings, and your net earnings determine the contribution, so the two chase each other. The IRS resolves the circularity with a reduced rate, and for a 25% plan the effective rate on net earnings works out to roughly 20%, applied after subtracting the deductible half of your self-employment tax. Publication 560 carries the worksheet that does this properly.

The practical version: a sole proprietor with $100,000 of net self-employment income is looking at something in the neighborhood of $18,500, not $25,000. Run the real numbers rather than the headline percentage, because contributing the 25% figure on self-employment income is one of the most common ways people create an excess contribution without meaning to.

Two more limits that matter. A standard SEP has no elective deferrals and no catch-up contributions, so being over 50 does not raise your ceiling. And SECURE 2.0 permits Roth SEP contributions, but only if your plan document allows them and your custodian actually supports them, which many still do not.

Deposited Is Not the Same as Deducted

The contribution has to be in the account by the deadline. Initiating a transfer on the deadline is not the same as the money arriving, and the IRS cares about the deposit.

This is where a September or October deadline gets people. Custodians are slow in exactly those weeks, for exactly this reason, and a transfer that normally clears in two days can take a week when everyone is doing the same thing. If you are opening a new SEP-IRA account at the same time, add account opening and funding verification on top of that.

Two weeks of margin is sensible. A day is not.

One more sequencing point. The deduction goes on the return for the year the contribution is for, not the year it was made. A contribution made in October 2026 for tax year 2025 belongs on the 2025 return. If you already filed that return without the contribution, you generally amend it to claim the deduction rather than trying to move the deduction forward a year.

If You Missed the Deadline

Two different situations, with different amounts of trouble.

You did not deposit anything. This is the simple case. You lose the deduction for that year and nothing else happens. The money stays in your business account, no penalty applies, and your attention should go to the current year, where a plan is still available and the deadline has not run.

You deposited it late. This one is not simple. A contribution that arrived after the deadline is not a valid contribution for that year, and it does not quietly become a contribution for the following year either. In the plan it is generally treated as an excess contribution, and excess contributions to a SEP carry a 10% excise tax reported on Form 5330 for each year they remain uncorrected. Nobody sends you a bill for it, which is why these tend to be discovered years later and stacked several deep.

The correction depends on how the deposit was coded, how long it has been sitting, and whether employees were affected. The small business excess contribution guide walks the paths, and the Small Business Excess Contribution Fix works out which correction applies to your situation and produces the deadlines and form references for it.

If the amount is large, or more than one year is involved, or employees are in the picture, this is a tax professional's job rather than a do-it-yourself one.

If You Have Employees

The deadline itself does not change. The entire SEP contribution is one employer contribution made against one tax return, so every participant is funded on the same date.

What does change is who has to be included. An employee generally has to be covered if they are at least 21, worked for you in three of the preceding five years, and earned at least $800 in 2026. That last figure is the section 408(k)(2)(C) threshold and it is low, which surprises people who assumed part-time or seasonal help would not qualify.

And the percentage has to be uniform. Whatever percentage of compensation you contribute for yourself, you contribute for every eligible employee. You cannot fund yourself at 20% and them at 5%.

Leaving eligible employees out is one of the most common SEP failures the IRS encounters, and it is expensive to unwind because the fix usually means making the missed contributions with earnings. If you have any staff at all, including part-time or former employees who worked three of the last five years, confirm the eligibility list before you fund.

Traps Worth Knowing About

Using April 15 when you file an 1120-S or a 1065. Your business return was due March 15. This is the single most common way a SEP deadline gets missed, because the owner is thinking about their personal return.

Assuming the personal IRA deadline and the SEP deadline work the same way. Extensions move one and not the other.

Filing late without an extension and assuming the SEP followed. It did not. Only a timely filed extension moves the date.

Contributing 25% of self-employment income. The effective rate on net earnings is closer to 20%, and using 25% creates an excess.

Initiating the transfer on the deadline. The money has to be there, not on its way.

Assuming a catch-up because you are over 50. A standard SEP has none.

Funding yourself and skipping the part-time employee. The compensation threshold is $800, not a living wage.

Missing that the deduction belongs to the earlier year. A contribution made this year for last year goes on last year's return, which may mean amending it.

Frequently Asked Questions