Number Salad, to Accompany Your Letter Soup, Madam

A plain-English guide to the numbers behind retirement plan compliance

You already know about the letter soup.

RPC. TPA. RIA. RPA. The retirement industry has spent decades building an alphabet that takes years to decode and even longer to say out loud at a dinner party without watching people’s eyes glaze over.

But underneath the letters lives an entirely separate language. One made of numbers.

401(k). 403(b). 404. 415. 3(16). Form 5500.

These aren’t just codes. They’re the operating framework behind every qualified retirement plan in the country. They define how plans are built, how they stay compliant, who’s responsible when something goes wrong, and how much money can actually go in. For plan sponsors and advisors, knowing what these numbers mean is the difference between navigating the system and being navigated by it.

Here’s your field guide.

The Foundation: Plan Types

401(k)

The one everyone’s heard of. A defined contribution plan that allows employees to defer a portion of their compensation into a retirement account, often with employer matching or profit sharing on top. Subject to annual contribution limits, nondiscrimination testing, and enough compliance requirements to keep an entire industry employed.

When someone says “retirement plan,” this is almost always what they mean.

403(b)

The 401(k)’s counterpart for nonprofits, public schools, and tax-exempt organizations. Structurally similar, different regulatory framework, different testing requirements, and a historical lean toward annuity-based investment options. Same goal. Different rulebook.

401(a)

Less a specific plan type, more a structural category. Profit-sharing plans, money purchase plans, and certain government or institutional arrangements often live here. Think of it as the container rather than the contents.

The Fiduciary Roles: Who Is Actually Responsible

This is where the numbers get personal, because these codes define who’s on the hook.

3(16) Fiduciary

The party responsible for plan administration. This is the role that oversees day-to-day compliance, signs and files the Form 5500, and ensures the plan is operating according to its own document. It’s not a ceremonial title. It carries real legal responsibility, and someone has to own it.

In many plans, this is where Asteri Collective member firms operate, taking on administrative fiduciary responsibility so the plan sponsor doesn’t have to.

3(21) Fiduciary

The investment advisor role. A 3(21) fiduciary recommends investment options and shares fiduciary responsibility with the plan sponsor, but doesn’t have full discretion over decisions. Think of it as guidance with shared accountability.

3(38) Fiduciary

Full investment discretion, delegated. A 3(38) fiduciary selects and manages the investment lineup and assumes responsibility for those decisions, which meaningfully reduces the plan sponsor’s liability in that area. When a plan sponsor wants to get out of the business of choosing funds, this is the arrangement that makes it possible.

The Compliance Framework: How Plans Stay Qualified

This is the part most plan sponsors would prefer to never think about. Which is exactly why they need an RPC.

404(a)

The foundational fiduciary standard under ERISA. Decisions must be made in the best interest of participants, with prudence, diversification, and reasonable costs as the guiding principles. Everything else in the compliance framework flows from this.

404(c)

The provision that protects plan sponsors when participants direct their own investments. When structured correctly, with a broad enough investment menu and proper participant disclosures, it shifts investment responsibility to the participant. “When structured correctly” is doing a lot of work in that sentence.

410(b)

Coverage testing. The requirement that ensures a retirement plan actually benefits a broad group of employees, not just the owners and executives at the top. It’s the IRS’s way of saying: if the tax advantages are available to everyone, the plan has to work for everyone.

401(a)(4)

Nondiscrimination testing for contributions. Works alongside 410(b) to ensure employer contributions are allocated fairly across the employee population. The two tests together are what prevent a retirement plan from functioning as a personal savings vehicle dressed up as a company benefit.

415 Limits

The annual cap on total contributions to a participant’s account, including employee deferrals, employer matching, and profit sharing combined. Adjusted annually by the IRS. This is the ceiling on how much can go into the plan in any given year.

402(g)

The separate cap specifically on employee salary deferrals. Distinct from the 415 limit, which covers everything. Knowing which limit applies where matters more than it might seem, especially for high earners trying to maximize contributions.

The Reporting Backbone

Form 5500

The annual report filed with the Department of Labor detailing plan assets, participant counts, and operational compliance. Required for most retirement plans. This is the formal record of what the plan did each year, and the document that becomes very important, very quickly, when an audit shows up.

The 3(16) fiduciary signs it. Which is one reason that role carries the weight it does.

What It All Adds Up To

None of these exist in isolation.

Plan design has to align with contribution limits. Contributions have to pass nondiscrimination testing. Investments have to meet fiduciary standards. Reporting has to reflect accurate, complete data. And underneath all of it, payroll data has to move correctly from the employer to the RPC to the recordkeeper, because if the inputs are wrong, every number downstream is wrong too.

That’s the part that doesn’t show up in the code citations.

A 415 violation doesn’t announce itself. An ADP testing failure doesn’t send a calendar invite. These things surface in year-end processes, correction filings, and audit requests, usually at the worst possible time, and usually traceable back to a data problem that was preventable.

The RPC’s Job in the Number Salad

Reading the numbers is not the hard part. Applying them is.

Retirement Plan Consultants translate regulations into actual plan design. They ensure the data flowing through the system supports compliance requirements. They coordinate across payroll providers, recordkeepers, and advisors so every rule is met in practice, not just on paper. And they anticipate the issues before they show up in testing, because the cost of prevention is always lower than the cost of correction.

The numbers define the rules of the game. The RPC makes sure the plan is actually playing by them.

The Two Languages of This Industry

Letters define the roles.

Numbers define the rules.

Most people in retirement planning spend their careers becoming fluent in one or the other. The firms that are genuinely indispensable to advisors, recordkeepers, and plan sponsors are fluent in both and can translate between them without making anyone feel like they need a decoder ring.

That’s what The Asteri Collective is built around. Not just knowing the framework, but executing within it. Every time, for every plan, without surprises.