Retirement plan compliance in 2026 brings a full calendar of critical deadlines that employers cannot afford to miss. From new SECURE 2.0 requirements to annual filings, contribution cutoffs, and participant notice timelines, each date plays a role in keeping your plan aligned with IRS rules and supporting a smooth year of administration.

To make planning easier, we have organized the major deadlines that affect 401(k), 403(b), and Defined Benefit plans, along with the changes arriving on January 1, including Roth catch-ups for high earners and eligibility for long-term part-time employees. Use this guide to map out your year, stay ahead of filings, and maintain a compliant and efficient retirement plan.

Click the image below to download an excel spreadsheet of these dates.

2026 Retirement Plan Compliance Task Definitions

Roth Catch-Up Rule Effective (January 1)
The SECURE 2.0 requirement for high earners takes effect at the start of 2026. Participants with prior-year wages above $145,000 must make all catch-up contributions on a Roth basis. Employers should confirm payroll and recordkeeping systems can distinguish between traditional and Roth catch-up elections to prevent reporting issues.

Long-Term Part-Time Employee Eligibility (January 1)
Employees who worked at least 500 hours in both 2024 and 2025 must be allowed to make elective deferrals beginning in 2026. This applies to 401(k) and 403(b) plans and may require updates to your eligibility tracking. Employers should ensure their payroll and HR systems correctly flag LTPT employees.

Form 1099-R Distribution Reporting (January 31)
Form 1099-R must be issued to anyone who received a retirement plan distribution in the prior year. This includes rollovers, refunds, RMDs, and other taxable events. Timely reporting helps participants file accurate tax returns and avoids IRS penalties for late or incorrect forms.

Form 1099-R Paper Filing Deadline (February 28)
If you choose to file 1099-R forms on paper, they must be submitted to the IRS by February 28. Paper filing is less common due to the IRS preference for electronic submission, but the deadline still applies for those who use it. Keep in mind that electronic filings allow more processing flexibility.

Electronic Filing Deadline for 1099-R (March 31)
Plans filing electronically must submit all 1099-R forms by March 31. Electronic filing is now the standard for most organizations and reduces the risk of processing delays. Confirm your file format and submission system are aligned well before the due date.

Employer Contribution Deadline for Pass-Through Entities (March 15)
S-Corporations and partnerships must deposit prior-year employer contributions by March 15 unless they filed for a tax extension. These contributions may include matching, profit-sharing, or defined benefit funding. Meeting this deadline helps maintain deductibility for the prior tax year.

RMD Deadline for 2024 Retirees (April 1)
Individuals who reached their required beginning date in 2024 must take their first RMD by April 1, 2026. After this first distribution, all subsequent RMDs follow the normal year-end schedule. Employers should assist participants with reminders to avoid IRS penalties.

Employer Contribution Deadline for C-Corps and Sole Proprietors (April 15)
C-Corporations and sole proprietors must deposit prior-year employer contributions by April 15 unless they have an approved tax extension. Meeting this deadline allows the business to deduct the contribution for the prior tax year. Contribution types vary by plan design and funding requirements.

ACA and Payroll Alignment Review (June 30)
Midyear is an ideal time to review ACA compliance, payroll coding, and eligibility alignment. This includes verifying measurement periods, plan eligibility for part-time workers, and any changes affecting hours tracking. Conducting this review midyear prevents surprises at year-end.

Form 5500 Due (July 31)
For calendar-year plans, Form 5500 and Form 8955-SSA must be filed by July 31 unless an extension is requested. These filings provide the Department of Labor and IRS with a detailed review of plan operations and participation. Timely submission avoids penalties and keeps the plan in good standing.

PBGC Premiums Due for Defined Benefit Plans (July 31)
Defined Benefit plan sponsors must submit their PBGC premium filings by July 31. Premiums include flat-rate and potentially variable-rate amounts based on plan underfunding. Accurate reporting is essential to avoid penalties and ensure the plan remains compliant.

Extended Contribution Deadline for Pass-Through Entities (September 15)
If an S-Corp or partnership filed for an extension, employer contributions for the prior plan year are due September 15. This extended window allows additional time to calculate profit-sharing and other funding. Contributions made by this date remain deductible for the prior year.

Summary Annual Report Due (September 30)
Plans must deliver the Summary Annual Report to participants by September 30, assuming the Form 5500 was filed on time. The SAR provides a readable overview of plan financial activity and compliance. Timely distribution supports transparency and participant communication.

Safe Harbor Notice Distribution Begins (October 1)
Employers offering Safe Harbor 401(k) plans must begin sending participant notices by October 1 for the upcoming plan year. These notices describe employer contributions, rights, and plan features. Providing them on time is essential to maintaining Safe Harbor status.

Extended Form 5500 Filing Deadline (October 15)
For plans that filed Form 5558 for an extension, the final deadline to submit Form 5500 is October 15. This extended timeline supports more complex plans or those awaiting final audit results. Meeting the deadline ensures the plan stays compliant.

Extended Employer Contribution Deadline for C-Corps and Sole Props (October 15)
If an extension was filed, C-Corporations and sole proprietors must deposit their prior-year employer contributions by October 15. These contributions remain deductible for the prior tax year if deposited by this date. Many businesses use the extension window to finalize financials before funding.

Auto Enrollment and QDIA Notices (December 1)
Plans with auto enrollment or a Qualified Default Investment Alternative must distribute annual notices by December 1 for the next plan year. These notices explain default investment options and participant rights. Providing them early ensures participants have time to make informed choices.

Plan Amendment Deadline (December 31)
Most SECURE 2.0 and discretionary plan amendments for 2026 must be adopted by December 31. This includes compliance updates and optional enhancements chosen during the year. Plan sponsors should coordinate with their TPA and advisor to ensure all required amendments are documented.

RMDs Due for 2026 (December 31)
All required minimum distributions for 2026 must be completed by December 31. Timely distribution prevents participants from incurring significant IRS penalties. Employers should ensure systems and communication processes support accurate year-end tracking.

Deferral and Match Verification (December 31)
Before year-end closes, employers should confirm that all employee deferrals and matching contributions have been posted correctly. This includes reconciling payroll, plan records, and any corrections for missed or late deposits. Verifying totals now reduces operational issues during annual testing.

When a business owner decides to offer a retirement plan, it’s a meaningful investment in the future, both for their team and for their own financial well-being. But with that decision comes a new set of responsibilities, deadlines, and regulatory requirements. That’s where a Third Party Administrator (TPA) like Mirador comes in.

What Is a TPA and Why Does It Matter?

A TPA, or Third Party Administrator, plays a critical role in the design, implementation, and ongoing management of retirement plans like 401(k)s. We’re the ones making sure the plan works, for your business, your people, and the IRS.

While the financial advisor focuses on investment options and the recordkeeper handles transactions, the TPA is responsible for how the plan is built and whether it complies with Department of Labor and IRS rules.

In the words of one Mirador expert featured in the video on this page:

“401(k) plans have to abide by a lot of IRS rules and regulations as well as DOL. And so there is a lot of compliance that comes into play. You have to file a Form 5500, you have to do nondiscrimination testing… you as a plan sponsor are responsible. Many plan sponsors, because it’s a lot of work, hire outside help, such as a 401(k) administrator or a third party administrator, where we are assisting you in making sure that you are in compliance with all of the regulations.”

The Business Owner’s Role: Plan Sponsor

When you offer a retirement plan, you’re not just doing something good for your team, you’re taking on the role of “plan sponsor.” That comes with fiduciary responsibility. You’re responsible for making sure the plan is fair, compliant, and properly managed.

This includes:

• Offering a plan that doesn’t discriminate in favor of highly compensated employees
• Filing required forms like the 5500
• Ensuring deadlines are met for contributions, notices, and testing
• Keeping the plan document up to date
  

But most business owners aren’t tax code experts. Nor should they be. That’s why TPAs exist.

What a TPA Does

At Mirador, we act as your technical expert and strategic partner in plan design. Here’s what that includes:

1. Plan Design

We don’t sell products, we build plans. That means we customize your 401(k) or defined benefit plan based on your goals: saving more for ownership, rewarding key employees, or staying ACA compliant. We ensure your plan structure maximizes flexibility and tax advantages.

2. Ongoing Compliance

We handle:

• Annual nondiscrimination testing
• Coverage and top-heavy testing
• Form 5500 preparation
• Required plan notices (Safe Harbor, QDIA, etc.)
• Contribution limit calculations

We stay on top of IRS and DOL updates so you don’t have to.

3. Consultation and Adjustments

Life changes, and so do businesses. We help you adjust your plan as your headcount, structure, or goals evolve.

Why “Third Party”?

The term “Third Party Administrator” simply reflects the relationship: the business owner (first party) hires an outside expert (third party) to fulfill the responsibilities of plan design and administration. It’s still your plan. You’re still responsible. But with a qualified TPA like Mirador, you’re not doing it alone.

When It Matters Most

Compliance issues often surface long after a plan is in place, during an IRS audit, a failed test, or a missed deadline. That’s why having a proactive TPA is so important. We don’t just check boxes. We anticipate issues, design around your goals, and guide you through the full lifecycle of your plan.Bottom line: You’re responsible for the plan, but you don’t have to manage it alone. At Mirador, we make sure your retirement plan works as hard as you do.

When business owners acquire or merge with another company, the headlines focus on valuation, synergies, and closing timelines. But quietly sitting in the background, often unnoticed until it’s too late, are legacy benefit plans, control group structures, and compliance traps that can derail your deal.

Retirement plans are consistently one of the most commonly overlooked elements in M&A transactions specifically, how control group and affiliated service group rules can create unexpected liability, compliance issues, and contribution obligations unless proactively addressed before the transaction closes.

Why Retirement Plans Must Be on the M&A Due Diligence List

“We work with successful business owners who acquire companies to grow, but they rarely think about how that impacts their existing retirement plan design.”

Buying or merging with another company may trigger IRS rules around control groups or affiliated service groups (ASGs). When that happens, your new business structure may require that all employees across both entities be tested together, and possibly receive contributions under your existing retirement plan.

If the acquired business has its own plan, things become even more complicated. There may be testing failures, required plan mergers, and transition rules to follow.

Understanding Control Groups in M&A

A control group exists when:

• You own 100% of your current business
• You acquire at least 80% of another business
  

These businesses are now considered one entity for retirement plan purposes, even if you operate them separately.

What it means:

• Employees in both companies must be included in nondiscrimination testing
• You may have to offer benefits to newly acquired employees
• If your current plan was designed for a lean staff, your contribution structure may need to change
  

Affiliated Service Groups: Less Ownership, Same Risks

An Affiliated Service Group doesn’t require 80% ownership. These groups are formed when:

• Two businesses work closely together to provide services
• Owners have overlapping management or operational control
• There’s a financial or service-based dependency between the entities

This can create a testing and compliance requirement even when the acquiring company owns less than 80% of the other.

Why Timing Matters

“We designed your plan for the life you had when we started, your structure, your staff, your ownership. If that changes, the plan needs to change too. But once you close the deal, your options become limited.”

Amendments can’t be retroactive. If the new company structure results in a failed nondiscrimination test, you may be required to fund employee contributions you hadn’t budgeted for. That’s why retirement plan review should happen before the transaction closes, not after.

M&A Compliance Checklist for Business Owners

Below is a checklist of what to review during any merger or acquisition:

Corporate and Operational Structure

• Ownership percentages post-transaction
• Whether common ownership triggers a Control Group or ASG
• Number of employees and employee classifications
  

Retirement Plan Considerations

• Whether the acquired company has an active plan
• Plan document availability and filing history (Form 5500)
• Testing compatibility and transition rules
• Whether a plan merger is advisable or necessary
  

Insurance and Risk Transfer

• Review or add Directors & Officers (D&O) coverage
• Errors & Omissions (E&O) policy alignment
• General liability, workers’ compensation, and commercial auto review
  

Employee Benefits

• Group health plan compatibility
• COBRA compliance transition
• Ancillary benefit obligations

Professionals You Should Notify (and Involve Early)

Too often, business owners loop in advisors after the deal closes. That’s too late for plan design. Here’s who should be at the table before the transaction is finalized:

• ERISA Attorney – for plan document review, compliance, and amendment timing
• Third Party Administrator (TPA) – for testing, filings, and plan design updates
• CPA – for tax implications of employer contributions and deduction strategy
• Wealth Advisor – to align plan changes with long-term retirement strategy
• Business Transaction Attorney – for deal structure, reps, and warranties related to benefit plans
• HR/Benefits Team or Consultant – for post-close onboarding and communication

Retirement Plans Aren’t a Footnote

If you’re acquiring or merging businesses and haven’t reviewed your retirement plan design, you’re missing a key element of due diligence. The IRS and DOL won’t give you a grace period because you were unaware.

Get ahead of it. Confirm whether control group or ASG rules apply. Test before you transact. Adjust your plan before it’s too late.

If you’re sponsoring a retirement plan, especially a 401(k), profit-sharing, or defined benefit plan, nondiscrimination testing isn’t optional. It’s a compliance requirement with real financial consequences for plan sponsors and owners who don’t pay attention.

Let’s explore what nondiscrimination testing is, why it exists, who it protects, and how smart plan design can help you pass, while still maximizing owner contributions.

What Is Nondiscrimination Testing?

Nondiscrimination testing (NDT) is a set of IRS-mandated compliance tests designed to ensure that retirement plans do not unfairly benefit highly compensated employees (HCEs) at the expense of rank-and-file employees.

It applies to:

• 401(k) and Safe Harbor plans
• Profit-sharing plans
• Defined benefit and cash balance plans
• Combination plans (e.g., DB/DC)

In short, if you’re offering retirement benefits, the IRS wants to ensure you’re not only enriching owners and top executives while leaving everyone else behind.

Why Was It Created?

Nondiscrimination testing exists to protect employees.

“It’s to make sure you’re not giving way too much money to your CEO and executives when compared to your staff,” says Alison Quesada, Partner at Mirador.

It ensures fairness and plan qualification. A plan that discriminates in favor of HCEs risks disqualification by the IRS, which can result in:

• Refunds of employee deferrals
• Required employer contributions
• Loss of tax-favored plan status
• Costly corrections or audits

Who Needs to Pay Attention to Nondiscrimination Testing?

NDT isn’t just the responsibility of your TPA, it affects:

• Business Owners: Because the structure of your contributions depends on passing these tests
• HR and Finance Leaders: Who handle compliance documentation and employee communication
• Advisors and CPAs: Who integrate retirement plan strategy into overall tax and compensation planning

If your plan includes both HCEs and rank-and-file employees (and most do), you’re subject to nondiscrimination testing.

Common Testing Areas

Here are the key tests most plans must pass annually:

ADP (Actual Deferral Percentage) Test

Compares how much HCEs and non-HCEs defer from their own pay into the 401(k).

ACP (Actual Contribution Percentage) Test

Compares employer matching and after-tax contributions between HCEs and non-HCEs.

Top-Heavy Testing

Determines whether key employees (e.g., owners, officers) hold more than 60% of total plan assets.

What Happens if You Fail?

Failing nondiscrimination testing can trigger:

• Refunds to HCEs, forcing owners and execs to pull money out of their accounts
• Additional employer contributions, to “rebalance” benefits to rank-and-file employees
• Penalties and potential loss of plan qualification if not corrected in time

The good news? These failures are often avoidable, with the right plan structure.

Smart Design: Combining Plans to Satisfy Compliance and Maximize Value

As Rachel Rosner explains in the video, one of the most powerful ways to pass NDT and support both owners and employees is by combining plan types:

“We call them DB/DC or CB/DC combination plans. So it’s a defined benefit plan paired with a 401(k) profit-sharing plan.”

How It Works:

• The defined benefit (DB) plan delivers large contributions for owners, designed around age, compensation, and years to retirement
• The 401(k) profit-sharing plan offers visible contributions for employees on familiar investment platforms like John Hancock or American Funds

This structure not only passes nondiscrimination testing, it also serves as:

• A tax strategy for owners
• A retention tool for employees
• A balanced benefit plan that satisfies IRS fairness rules

“While we say we set these plans up for the owners, it still is for the owners,” says Rosner. “But the employees get real value too.”

Watch the Video: Nondiscrimination Testing, Explained

Mirador Partners Alison Quesada and Rachel Rosner break down how testing works, who it impacts, and how we structure combination plans to meet compliance and contribution goals.