Solo 401(k) Compliance Calendar: Every Deadline & Form You Can’t Miss

Owning your own business gives you tremendous flexibility, but it also places every compliance responsibility for your Solo 401(k) squarely on your shoulders. Missing even one IRS due date can turn a valuable tax shelter into a costly tangle of penalties. Below is a month-by-month guide that demystifies each filing, contribution, and document deadline so you can keep your retirement plan on the right side of the rules and focused on building wealth.

December 31: Establish or Amend the Plan

For most owners who operate as an S-corp, C-corp, LLC, or partnership, your Solo 401(k) must be adopted by the last day of the tax year—December 31—to make salary-deferral contributions for that same year. Sole proprietors have a little extra breathing room, but the safest course is still to sign plan documents before New Year’s Eve to lock in maximum flexibility.[1]IRS

April 15 (or Tax-Filing Day): Employee Deferral Grace Period for Sole Proprietors

The SECURE 2.0 Act gave unincorporated owners until their personal filing deadline (normally April 15) to both open a plan and make employee deferrals for the prior year, provided the plan existed by that date.[2] MySolo401k For corporations, the salary-deferral election must still be on file by December 31, even though the actual deposit can wait until the company’s return is filed.

Tax Return Due Date plus Extensions: Employer Contributions

Whether you’re filing as a sole proprietor or through an entity, the employer side of your Solo 401(k) contribution can be made up to the due date of that return—including a six-month extension if you file Form 4868 (individual) or Form 7004 (business).[3] Accounting Insights This means many owners effectively have until September 15 (S-corp/partnership) or October 15 (sole proprietor or C-corp on extension) to fund the profit-sharing portion.

January 31: Forms 1099-R to Recipients and Form 945 to the IRS

If your plan made any distributions or Roth conversions last year, each recipient must receive Form 1099-R by January 31. Paper Form 945, which summarizes any federal tax you withheld from those distributions, is also due to the IRS the same day unless deposits were made on time, in which case you have until February 10.[4] TaxZerone.com rsgweb.com

February 28 (Paper) or March 31 (E-File): Forms 1099-R to the IRS

Once participants have their copies, you still need to send the 1099-R information to the IRS. Paper filers must mail by February 28; electronic filers get until March 31.[5]IRS

July 31: Form 5500-EZ Annual Return

When total plan assets top $250,000 on December 31—or if you are closing the plan—file Form 5500-EZ by July 31. This brief information return confirms your plan’s balance and investment mix. Failing to file can trigger penalties of $250 per day, capped at $150,000.[6] Safeguard Advisors

Daily Cash-Flow Discipline: Deposit Salary Deferrals Promptly

While the IRS lets employer contributions wait until the tax return is due, employee contributions you withhold from your own compensation must hit the plan as soon as they can be “reasonably segregated” from business assets. For most Solo 401(k)s this translates to a best practice of moving money within a few days of paying yourself, even though the large-plan 15-day safe harbor does not technically apply. Staying prompt avoids any hint of self-dealing.

Ad Hoc: Participant Loans, Hardship Distributions, and Rollovers

Issuing a participant loan? Draft and execute a promissory note before cutting the check, and adhere to quarterly amortization. Hardships require that the plan document allow them and that you document the immediate need. Direct and indirect rollovers are not technically deadline driven, but you must supply the participant a written “special tax notice” at least 30 days before an eligible rollover distribution unless they waive the period.

December 31 2026: SECURE & CARES Act Plan Amendments

Congress has passed multiple retirement overhauls since 2019, and plan documents need to catch up. Pre-approved Solo 401(k)s must be amended for the SECURE, CARES, and SECURE 2.0 changes by December 31 2026. Waiting risks disqualification of the entire plan.[7]Spencer Fane

April 1 of the Year After You Turn 73 (or 75 in 2033): First RMD for 5 %-Owners

If you are still working for your own company at age 73, you are considered a 5 % owner and cannot delay required minimum distributions past April 1 of the following year. Every subsequent RMD is then due by December 31. Missing an RMD invites an excise tax of up to 25 %, reduced to 10 % if corrected quickly.

Ongoing Documents to Keep on File

Retain your signed plan document, any amendments, trust statements, loan notes, valuation reports, and proof of timely contributions for at least seven years. Should the IRS ever audit the plan, good records turn a stressful request into routine correspondence.

Why Staying Ahead Matters

The Solo 401(k) already enjoys generous contribution limits—as high as $69,000 in 2024, plus a $7,500 catch-up if you are 50 or older.[8]Investopedia By monitoring the compliance calendar, you preserve these high limits, protect hard-earned tax deductions, and avoid penalties that can easily rival what you meant to save for retirement.

How Westlight Wealth Helps

Tracking paperwork may not be why you went into business, but it is part of protecting the nest egg you are building. At Westlight Wealth, we maintain a proactive checklist for every Solo 401(k) we advise, remind clients before each filing window opens, and coordinate with tax professionals so nothing falls through the cracks. If you prefer spending your evenings growing your company instead of reading IRS instructions, let us steward the deadlines while you focus on profits. Contact us today to schedule a complimentary review of your Solo 401(k) plan.

Sincerely,

Gustaf Rounick, CFP®

Works Cited

[1] IRS, “One-Participant 401(k) Plans,” https://www.irs.gov/retirement-plans/one-participant-401k-plans

[2] MySolo401k.net, “How Late Can You Make a Solo 401(k) Contribution?” https://www.mysolo401k.net/how-late-can-you-make-a-solo-401k-contribution/

[3] AccountingInsights.org, “When Are Solo 401k Contributions Due?” https://accountinginsights.org/when-are-solo-401k-contributions-due/

[4] TaxZerone, “Form 1099-R Instructions & Deadlines,” https://www.taxzerone.com/resources/information-returns/form-1099-r-instructions/ and IRS, “Form 945 Instructions,” https://www.irs.gov/instructions/i945

[5] IRS, “Instructions for Forms 1099-R and 5498,” https://www.irs.gov/instructions/i1099r

[6] Solera Plan Services, “Solo 401(k) 5500-EZ Filings Due July 31st,” https://ira123.com/solo-401k-5500-ez-filings-due-date/

[7] Spencer Fane LLP, “IRS Announces New Plan Amendment and Cycle 4 Restatement Deadlines,” https://www.spencerfane.com/insight/irs-announces-new-plan-amendment-and-cycle-4-restatement-deadlines/

[8] Investopedia, “A 401(k) Plan for the Small Business Owner,” https://www.investopedia.com/retirement/401k-plans-small-business-owner/

Disclosures:

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