IRC 401(a) and 401(k): Qualified Plan Requirements and CODA Mechanics

Overview: The Qualified Plan Framework

A tax-qualified retirement plan under IRC 401(a) is the centerpiece of employer-sponsored retirement benefit design. Qualification confers a substantial tax advantage: employer contributions are deductible when made, investment earnings accumulate without current tax, and participants are not taxed until distribution. In exchange for those benefits, a plan must satisfy a detailed and interlocking set of statutory and regulatory requirements enforced by both the Internal Revenue Service and the Department of Labor under ERISA.

For practitioners advising plan sponsors during plan design and amendment season, the qualification rules fall into two broad categories. First, the foundational IRC 401(a) requirements apply to every qualified defined contribution and defined benefit plan. Second, if the plan includes a cash-or-deferred arrangement (CODA), the additional IRC 401(k) requirements overlay the baseline rules and bring their own testing, contribution, and now OBBBA-driven automatic-enrollment obligations.

The One Big Beautiful Act (OBBBA), enacted in 2025, made significant changes to 401(k) plan requirements in three areas: mandatory automatic enrollment, expanded hardship distributions, and the long-term part-time employee eligibility window. All three changes are recently enacted; implementation guidance may be pending. Verify at IRS.gov and consult independent counsel before advising clients on plan amendments or operational changes related to any of these provisions.

IRC 401(a) Core Qualification Requirements

IRC 401(a) sets out the conditions a plan must satisfy to be a "qualified" plan. Failure to satisfy any material condition can result in disqualification, which would cause all contributions to become immediately includible in participants' income and eliminate the employer's deduction. The IRS administers a voluntary correction program (the Employee Plans Compliance Resolution System, EPCRS) for correcting plan defects without disqualification; verify the current EPCRS procedures at IRS.gov.

1. The Exclusive Benefit Rule

Under IRC 401(a), the plan must be established for the exclusive benefit of employees or their beneficiaries. This means plan assets cannot revert to the employer except in limited, prescribed circumstances (for example, a contribution made by mistake of fact, or upon plan termination after all liabilities to participants have been satisfied). The exclusive benefit rule also animates the prohibited transaction restrictions under ERISA Section 406 and IRC 4975, which restrict self-dealing and conflicts of interest in plan asset management. Verify current exclusive benefit requirements and prohibited transaction exemptions at IRS.gov.

2. The Permanence Requirement

A qualified plan must be a permanent and ongoing program. Treasury Regulations under IRC 401 provide that a plan will be considered terminated, and thus potentially never having been qualified, if it is abandoned shortly after establishment without a valid business reason. A plan terminated within a few years of adoption with most of the benefit accruing to owners or HCEs raises a serious permanence concern. Plan sponsors should document business reasons for any early plan termination and consult ERISA counsel. Verify current permanence standards and IRS guidance at IRS.gov.

3. The Definite Written Program Requirement

The plan must be evidenced by a formal written document that sets out all material terms: eligibility conditions, contribution formulas, vesting schedules, distribution options, and amendment procedures. Reliance on a prototype or volume submitter document approved by the IRS satisfies this requirement provided the plan is maintained in operation in accordance with the document's terms. Operational failures -- running the plan in a manner inconsistent with the written document -- are the most common source of qualification failures identified in IRS audits. Verify current written plan requirements and EPCRS correction methods at IRS.gov.

4. The Trust Requirement

Plan assets must generally be held in a qualifying trust organized in the United States for the exclusive benefit of employees and their beneficiaries. The trust must be irrevocable (with limited exceptions for employer contributions made by mistake of fact) and must prohibit diversion of trust assets to any purpose other than participant benefits before all plan liabilities have been satisfied. Group annuity contracts issued by insurance companies may satisfy the trust requirement in certain circumstances. Verify current trust requirement alternatives and IRS approval procedures at IRS.gov.

5. Coverage and Vesting Requirements

A plan must cover a sufficient percentage of employees under the IRC 410(b) minimum coverage tests (the ratio percentage test or the average benefits test) and must provide vesting in employer contributions that is at least as rapid as the statutory schedules under IRC 411 (generally three-year cliff or two-to-six-year graded for matching contributions, with different schedules for other contributions). Verify current coverage and vesting requirements at IRS.gov.

IRC 401(a)(4) Nondiscrimination: ADP/ACP Testing and Safe Harbors

IRC 401(a)(4) requires that contributions or benefits under the plan not discriminate in favor of highly compensated employees (HCEs). The nondiscrimination rules are among the most operationally intensive requirements in qualified plan administration and are the primary driver of the safe harbor plan design market.

Highly Compensated Employee Definition: IRC 414(q)

An HCE under IRC 414(q) is any employee who (a) was a 5%-or-more owner at any time during the current or preceding plan year, or (b) received compensation from the employer in excess of a statutory threshold during the preceding year. Research indicates the 2026 compensation threshold for HCE status is $160,000; verify the current inflation-adjusted threshold at IRS.gov. The top-paid group election and calendar-year data elections affect which employees fall into the HCE category in a given plan year. Non-highly compensated employees (NHCEs) are all participants who are not HCEs. Verify the current HCE definition and election options at IRS.gov.

The ADP Test

For 401(k) plans, elective deferrals are tested annually through the Actual Deferral Percentage (ADP) test. The ADP for a group is the average of the individual actual deferral ratios (elective deferrals divided by compensation) for all eligible employees in that group. The HCE group's ADP may not exceed the greater of:

• 125% of the NHCE ADP, or
• The lesser of 200% of the NHCE ADP, or the NHCE ADP plus 2 percentage points.

If the HCE group fails the ADP test, the plan must either distribute excess contributions to the HCEs (with income) within 2.5 months after the close of the plan year to avoid a 10% excise tax, or recharacterize elective deferrals as after-tax employee contributions if permissible under the plan. Verify current ADP correction procedures and excise tax rules at IRS.gov.

The ACP Test

Employer matching contributions and employee after-tax contributions are tested through the Actual Contribution Percentage (ACP) test, which applies an identical mathematical structure to the ADP test. Plans with both ADP and ACP failures must address each independently. Safe harbor plans that satisfy the matching or nonelective safe harbor requirements are exempt from ADP testing and, under certain conditions, from ACP testing for matching contributions. Verify current ACP safe harbor conditions at IRS.gov.

Safe Harbor Designs

Two primary safe harbor structures allow a 401(k) plan to bypass ADP and ACP testing entirely, provided the plan satisfies prescribed contribution, notice, and vesting requirements:

• Traditional Safe Harbor (IRC 401(k)(12)): The employer must contribute either (a) a matching contribution equal to 100% of elective deferrals up to 3% of compensation plus 50% of elective deferrals from 3% to 5% of compensation (the basic match), or (b) a nonelective contribution of at least 3% of compensation to all eligible NHCEs, regardless of whether they defer. The plan must provide advance notice to employees. Verify the current safe harbor matching formula and notice requirements at IRS.gov.
• QACA (Qualified Automatic Contribution Arrangement, IRC 401(k)(13)): The QACA safe harbor requires automatic enrollment at a minimum initial default rate, annual automatic escalation to at least 6% (verify the current minimum escalation target at IRS.gov), a reduced employer matching formula (100% of deferrals up to 1% of compensation plus 50% of deferrals from 1% to 6% -- verify at IRS.gov), and two-year cliff vesting for the safe harbor contributions. OBBBA significantly amended the QACA requirements; see Section 7 below. Verify at IRS.gov and consult independent counsel, as these provisions are recently enacted and implementation guidance may be pending.

IRC 401(a)(17) Compensation Limit

IRC 401(a)(17) limits the annual compensation that may be taken into account under any qualified plan. Research indicates the 2026 limit is $350,000; verify the current inflation-adjusted limit at IRS.gov. This limit affects every plan formula that references compensation as an input.

Impact on Benefit and Contribution Formulas

In a defined benefit plan, the IRC 401(a)(17) limit caps the compensation used to compute the benefit accrual. A final-average-pay formula that replaces 60% of the final three-year average salary is effectively limited to 60% of the capped compensation, not 60% of actual pay above the threshold. In a defined contribution plan, the limit caps the base to which any percentage formula is applied. A 10% profit-sharing formula generates a maximum employer contribution of $35,000 (10% of $350,000; verify the current limit), regardless of a participant's actual compensation above the threshold.

The IRC 401(a)(17) limit also interacts with the IRC 415 annual additions limit (discussed in Section 5) and with the compensation definition used in nondiscrimination testing. Plans must expressly incorporate the limit in their plan document -- a formula that references compensation without capping it at the statutory limit creates an operational failure if applied to compensation above the threshold. Verify the current limit and plan document language requirements at IRS.gov.

Executives and Nonqualified Plans

The compensation cap means that highly paid executives cannot accumulate benefits in a qualified plan proportional to their compensation. This gap is the primary driver of nonqualified deferred compensation arrangements under IRC 409A. Practitioners advising plan sponsors with highly compensated executives must understand the interplay between the qualified plan benefit, the IRC 401(a)(17) cap, and any nonqualified arrangement layered on top. Verify current IRC 409A requirements and the interaction with qualified plan benefits at IRS.gov.

IRC 415 Annual Additions Limit

IRC 415(c) limits the total annual additions to a defined contribution plan for any participant in a limitation year. Research indicates the 2026 limit is $70,000; verify the current inflation-adjusted limit at IRS.gov. "Annual additions" means the total of employer contributions, employee elective deferrals, and employee after-tax contributions allocated to a participant's account during the limitation year. Catch-up contributions that qualify under IRC 414(v) (the age-50 catch-up and the OBBBA-era age 60-63 super catch-up) are not included in annual additions for IRC 415 purposes; verify the current catch-up exclusion rules at IRS.gov.

The Three-Part Test

Annual additions for a participant in any limitation year may not exceed the least of:

1. The dollar limit (research indicates $70,000 for 2026; verify the current inflation-adjusted limit at IRS.gov);
2. 100% of the participant's compensation (as defined under IRC 415(c)(3)) for the limitation year; or
3. Any other applicable limit specified in the plan document.

The 100%-of-compensation limit is most relevant for part-time employees and lower-paid workers whose total annual additions could otherwise exceed their full-year compensation. Verify the current IRC 415(c)(3) compensation definition and any safe harbor compensation definitions at IRS.gov.

Controlled Group Aggregation

A participant who is employed by two or more members of a controlled group under IRC 414(b) or (c), or an affiliated service group under IRC 414(m), is treated as employed by a single employer for IRC 415 purposes. All annual additions from all defined contribution plans of the controlled group must be aggregated and tested against the single IRC 415(c) limit. This aggregation rule creates traps for plan sponsors operating through multiple entities: a participant with a large account in one entity's plan may have limited room for contributions in another entity's plan. Verify the current controlled group and affiliated service group rules at IRS.gov.

IRC 401(k) CODA Mechanics and Elective Deferral Limits

A cash-or-deferred arrangement (CODA) is a plan provision under which an eligible employee may elect to have the employer contribute a portion of compensation to the plan on a pre-tax basis, rather than receiving that amount in cash. IRC 401(k) provides the statutory framework for CODAs and sets out the requirements that must be satisfied for elective deferrals to be excluded from the employee's gross income under IRC 402(e)(3).

The Basic CODA Requirement

Under IRC 401(k)(2), a CODA is qualified only if the employee's right to the deferred amount is nonforfeitable. Elective deferrals must be 100% vested at all times -- the employer may not impose a vesting schedule on amounts the employee has deferred. This immediate vesting requirement distinguishes elective deferrals from employer matching and nonelective contributions, which may be subject to vesting schedules. Verify the current vesting rules for each contribution type at IRS.gov.

Elective Deferral Limit: IRC 402(g)

The annual limit on an employee's elective deferrals across all 401(k), 403(b), and SIMPLE plans is set by IRC 402(g). Research indicates the 2026 limit is $23,500; verify the current inflation-adjusted limit at IRS.gov. This is a per-person limit, not a per-plan limit. An employee who participates in a 401(k) plan and a SIMPLE IRA simultaneously must aggregate deferrals across both and stay within the IRC 402(g) limit (subject to the SIMPLE IRA's own lower limit). Deferrals in excess of the limit are included in the employee's gross income for the year of excess and, unless timely corrected, may also be taxed a second time at distribution. Verify the current IRC 402(g) limit, aggregation rules, and excess deferral correction procedures at IRS.gov.

Age-50 Catch-Up Contributions: IRC 414(v)

IRC 414(v) permits participants who are age 50 or older by the end of the calendar year to make additional elective deferrals (catch-up contributions) above the IRC 402(g) limit, provided the plan permits them. Research indicates the 2026 age-50 catch-up limit for 401(k) plans is $7,500; verify the current inflation-adjusted limit at IRS.gov. Adding the catch-up to the standard limit: a participant age 50 or older in 2026 may defer up to $31,000 in a 401(k) plan (verify all limits at IRS.gov). Catch-up contributions are not subject to ADP testing and are not counted as annual additions for IRC 415 purposes. Verify the current catch-up rules and exclusions at IRS.gov.

Age 60-63 Super Catch-Up: OBBBA/SECURE 2.0

SECURE 2.0 Act, as amended or implemented through OBBBA, introduced a higher catch-up contribution limit for participants who attain age 60, 61, 62, or 63 during the calendar year. Research indicates this super catch-up is $11,250 (or 150% of the regular age-50 catch-up amount, whichever is greater; verify at IRS.gov) for 401(k) plans in 2026. This means a participant turning 61 in 2026 may be eligible to defer up to $34,750 ($23,500 standard + $11,250 super catch-up; verify all limits at IRS.gov). The super catch-up replaces the standard age-50 catch-up for participants in the 60-63 age window; it does not stack on top of the age-50 catch-up. Verify at IRS.gov and consult independent counsel, as these provisions are recently enacted and implementation guidance may be pending.

Roth catch-up requirement for high earners. SECURE 2.0 Act also requires that catch-up contributions made by participants whose prior-year wages from the employer exceed a statutory threshold (research indicates $145,000; verify the current threshold at IRS.gov) must be made on a Roth (after-tax) basis for plan years beginning after December 31, 2023. Plans that do not offer a Roth contribution feature must add one to remain compliant for high earners making catch-up contributions. The IRS has issued transition relief extending the effective date; verify the current operative date and any remaining transition guidance at IRS.gov before amending plan documents or changing payroll processes.

OBBBA: Mandatory Automatic Enrollment Under IRC 401(k)(13)

One of the most operationally significant changes in recent retirement plan legislation is the OBBBA's expansion of the mandatory automatic enrollment requirement. Prior law permitted but did not require automatic enrollment; the OBBBA amendments to IRC 401(k)(13) change the calculus for new plans.

QACA Requirements Under OBBBA

A QACA under IRC 401(k)(13), as amended by OBBBA, must incorporate the following features:

• Automatic enrollment: New eligible employees are automatically enrolled in the plan at a default contribution rate without requiring an affirmative election.
• Initial default rate and escalation band: The initial default rate must fall within a prescribed range. The OBBBA amended the escalation band so that the contribution rate must automatically increase to a level within the range of 3% to 15% of compensation. Verify the current initial rate floor and the maximum automatic escalation target at IRS.gov, as guidance on the exact band parameters may be pending.
• Automatic escalation: If the participant does not make an affirmative election, the default rate increases automatically each year until it reaches the top of the prescribed band (or the participant's own elected rate). The escalation schedule must be set out in the plan document. Verify the current minimum escalation increment and any safe harbor escalation schedules at IRS.gov.
• Opt-out right: Participants must be given a meaningful opportunity to opt out of automatic enrollment or to elect a different contribution rate, including zero. The opt-out right does not waive the requirement that new eligible employees be auto-enrolled initially. Verify current opt-out notice timing and content requirements at IRS.gov.
• Safe harbor employer contribution: The QACA requires a minimum employer contribution -- either a matching contribution (100% of deferrals up to 1% of compensation, plus 50% of deferrals from 1% to 6% of compensation) or a nonelective contribution of at least 3% of compensation for all eligible NHCEs. Verify the current QACA contribution formulas and any OBBBA modifications at IRS.gov and consult independent counsel, as these provisions are recently enacted and implementation guidance may be pending.
• Vesting: QACA safe harbor contributions are subject to a two-year cliff vesting schedule. Elective deferrals remain 100% immediately vested.

Grandfathering for Existing Plans

Plans established before the OBBBA effective date for the mandatory QACA requirement may be eligible for grandfathering from the new mandate. The conditions, scope, and duration of any grandfathering protection, as well as the plan amendment deadline, must be confirmed at IRS.gov and with independent ERISA counsel. Verify at IRS.gov and consult independent counsel, as these provisions are recently enacted and implementation guidance may be pending.

OBBBA: Hardship Distribution Expansion Under IRC 401(k)(14)

OBBBA amended IRC 401(k)(14) to expand the events that permit a hardship distribution from a 401(k) plan. Prior regulatory guidance under Treasury Regulation 1.401(k)-1(d)(3) defined a limited set of safe harbor hardship events, and personal casualty loss distributions generally required a federally declared disaster. OBBBA removed the disaster-declaration requirement for certain casualty loss hardships.

Key Features of the Expanded Hardship Rule

• Personal casualty loss without disaster declaration: Under the OBBBA amendment, a participant may take a hardship distribution to cover personal casualty losses (as generally defined by reference to IRC 165(h)) without requiring a presidentially declared federal disaster. This aligns the 401(k) hardship rule with the direction Congress has taken in other relief provisions. Verify the exact scope of the casualty loss definition and any limitations at IRS.gov and consult independent counsel, as these provisions are recently enacted and implementation guidance may be pending.
• Self-certification: The OBBBA hardship expansion includes a self-certification procedure that permits participants to certify the existence of the hardship condition without providing third-party documentation to the plan administrator, reducing plan operational burden. Plan administrators retain the right to require substantiation if they have actual knowledge that the self-certification is inaccurate. Verify the current self-certification requirements and anti-fraud safeguards at IRS.gov.
• Anti-abuse provisions: The statute includes anti-abuse provisions designed to limit repeated, coordinated, or fraudulent hardship claims. The IRS may issue guidance defining the scope of these provisions. Verify at IRS.gov and consult independent counsel.

Long-Term Part-Time Employee Rule: IRC 401(k)(2)(D) as Amended

The long-term part-time (LTPT) employee eligibility rule, introduced by SECURE Act 2019 and revised by SECURE 2.0 Act, was again amended by OBBBA to accelerate the eligibility window for part-time employees to participate in 401(k) plans as elective deferral contributors.

Two-Year/500-Hour Eligibility Rule

Under IRC 401(k)(2)(D) as amended by OBBBA, a 401(k) plan must allow an employee to make elective deferrals if the employee has completed at least 500 hours of service in each of two consecutive 12-month periods. The 12-month periods are measured under the plan's eligibility computation period rules. Employees who qualify under the LTPT rule need not satisfy the plan's standard eligibility requirements (which might require 1,000 hours or one year of service). Verify the current LTPT eligibility rules, computation period rules, and any interaction with plan eligibility waiting periods at IRS.gov.

Scope: Deferral Eligibility Only

The LTPT rule grants LTPT employees the right to make elective deferrals. It does not require the plan to provide LTPT employees with employer matching or nonelective contributions (though the plan may choose to do so). Plan sponsors should review their contribution formulas and confirm whether LTPT employees are eligible for employer contributions under the plan's written terms. If LTPT employees are eligible for employer contributions, they must also be tested for nondiscrimination purposes. Verify the current contribution scope of the LTPT rule at IRS.gov.

Vesting for LTPT Employees

LTPT employees who receive employer contributions are subject to modified vesting rules. Under the OBBBA amendments, each 12-month period in which an LTPT employee completes at least 500 hours of service is counted as a vesting year, even for periods before the employee met the LTPT eligibility threshold. This protects LTPT employees from losing unvested employer contributions they would have earned over the multi-year eligibility window. Verify the current LTPT vesting accrual rules and any IRS guidance on hours-based vs. elapsed-time vesting methods at IRS.gov and consult independent counsel, as these provisions are recently enacted and implementation guidance may be pending.

Top-Heavy Rules: IRC 416

A qualified plan is "top-heavy" under IRC 416 if, as of the determination date, more than 60% of the aggregate present value of accrued benefits (in a defined benefit plan) or account balances (in a defined contribution plan) belong to "key employees." The top-heavy rules impose minimum contribution or benefit obligations designed to ensure that rank-and-file employees receive a meaningful benefit when the plan disproportionately favors owners and officers.

Key Employee Definition

Under IRC 416(i), a key employee is any employee (including former employees and beneficiaries) who at any time during the plan year was:

• An officer of the employer with annual compensation exceeding a statutory threshold (research indicates the 2026 officer compensation threshold is $230,000; verify the current inflation-adjusted limit at IRS.gov);
• A 5%-or-more owner of the employer; or
• A 1%-or-more owner with annual compensation exceeding $150,000 (this threshold is not indexed; verify at IRS.gov).

For purposes of the 5% and 1% ownership tests, stock attribution rules under IRC 318 and the IRC 416(i) ownership attribution rules apply. Verify the current key employee definition, attribution rules, and compensation thresholds at IRS.gov.

Minimum Contribution Obligation

If a defined contribution plan is top-heavy for a plan year, the employer must contribute a minimum amount to each non-key employee's account equal to 3% of each non-key employee's compensation for the year (or, if the highest contribution rate for any key employee is less than 3% of compensation, that lower rate applies). Elective deferrals made by non-key employees do not count toward the top-heavy minimum. Employer matching contributions may count toward the minimum if the plan document provides for them to count. Verify the current top-heavy minimum rules and counting provisions at IRS.gov.

Interaction with Safe Harbor Plans

A plan that satisfies the traditional safe harbor or QACA safe harbor contribution requirements is generally exempt from the top-heavy minimum contribution requirement for the plan year in which the safe harbor applies, provided the plan makes no additional nonelective contributions for the year beyond the safe harbor contribution. This is one of the most administratively valuable features of safe harbor plan design: it eliminates both ADP/ACP testing and the top-heavy minimum in a single structural election. Verify the current safe harbor top-heavy exemption conditions, including any OBBBA modifications to the QACA safe harbor, at IRS.gov.

IRC 401(k) Plan Termination

When a 401(k) plan terminates, participants' account balances must be distributed (or rolled over) or the plan must continue in a frozen state maintaining all benefits for existing participants without accepting new contributions. The Internal Revenue Code and ERISA impose specific requirements on plan terminations to protect participant benefits and maintain qualified status through the termination date.

Distribution Rules on Termination

IRC 401(k)(10) provides that, upon plan termination, a participant's entire account balance (including the vested portion of any employer contributions) may be distributed in a lump sum or rolled over to an eligible retirement plan, even if the participant has not otherwise experienced a distributable event (such as reaching age 59.5, separation from service, or disability). The plan must comply with the IRC 411(d)(6) anti-cutback rules, which prohibit eliminating an optional form of benefit accrued under the plan. Verify the current plan termination distribution rules and rollover requirements at IRS.gov.

Partial Termination and Immediate Vesting

If a plan partially terminates (typically defined as a significant reduction in the number of plan participants due to employer action, which the IRS often constructs as a 20% or greater reduction), all affected participants become immediately 100% vested in their employer-contribution account balances as of the partial termination date. The partial termination analysis is fact-intensive and has been the subject of significant IRS guidance and litigation. Verify the current partial termination rules, the IRS's percentage-based presumption, and the employee-count measurement methodology at IRS.gov before advising plan sponsors on workforce restructuring that could trigger partial termination.

Interaction with IRC 1374 for S-Corp Conversions

When an employer converts from a C corporation to an S corporation, the plan termination decision intersects with the IRC 1374 built-in gains (BIG) tax. A C corporation that terminates its qualified plan before converting to S-corp status may trigger a reversion of residual plan assets to the employer if the plan has a surplus; that reversion is subject to both corporate income tax and a 50% excise tax under IRC 4980. The plan termination and the IRC 1374 recognition period for appreciated assets held at conversion must be analyzed in coordination. Verify the current IRC 1374 built-in gains recognition period and any plan termination interactions at IRS.gov before advising clients on C-to-S conversions involving qualified plans.

Plan-Type Comparison Table

All limits cited below are research-based figures for 2026; verify the current inflation-adjusted limits at IRS.gov before advising any client. All plan-design features and regulatory requirements should be confirmed with plan counsel and the governing plan document.

All dollar limits, contribution formulas, and plan design requirements cited above are research-based figures for 2026 and must be verified at IRS.gov before use in plan documents or client advice. OBBBA provisions (QACA mandatory enrollment, hardship expansion, LTPT two-year rule) carry additional uncertainty; consult independent counsel as implementation guidance may be pending.