ACP Testing Explained: Which Contributions Count and How the Test Works
Understand ACP testing inputs, how matching and after-tax contributions differ from ADP inputs, and how to build a reliable annual workflow.
ACP testing compares the matching and after-tax contribution percentages of HCEs and NHCEs; it is not a second name for the elective-deferral test.
ACP Testing Explained: Which Contributions Count and How the Test Works matters because annual compliance work is only as reliable as the employee, payroll, ownership, and plan-document data behind it. This guide gives plan sponsors an operational way to understand the question, ask better questions of their administrator, and document decisions without treating a general article as individualized tax, legal, actuarial, investment, or compliance advice.
At a glance
- Core question: What data and classification rules control this result?
- Focus: Reconcile the plan document, payroll, and participant file before acting.
- Reading path: Define the rule, compare the inputs, then build a documented workflow.
Define the issue
For ACP, calculate each eligible participant’s matching and after-tax contributions as a percentage of testing compensation, then average the percentages by employee group. [1]
For a sponsor, the practical definition starts with the plan document. It identifies the plan year, eligibility rules, compensation definition, contribution sources, and administrative elections that shape the calculation. A service provider can calculate from a file, but the sponsor remains responsible for supplying accurate operational facts and noticing when a file does not match the plan’s terms.
That distinction is especially important after a business change. A new payroll system, acquisition, owner change, merger, rehire population, or revised match formula can alter the information that should reach the annual review. The best time to resolve an ambiguity is when the underlying records are still easy to trace—not after a final report creates a surprise.
How the mechanism works
The contribution universe is the key distinction: ADP focuses on elective deferrals, while ACP focuses on matching and after-tax employee contributions. A payroll export that treats all deposits alike can produce a persuasive-looking but wrong test. [1]
Think of the process as a chain: source records determine participant classification; classification and plan terms determine the testing population; payroll and account records provide amounts; and the resulting calculation informs a sponsor decision. A break at any link can make a result unreliable. That is why a documented input review is a control, not administrative busywork.
Compare the important inputs
| Input | Question to ask | Why it matters |
|---|---|---|
| Plan document | Which definitions and elections apply? | It sets the permitted calculation and correction path. |
| Participant file | Who belongs in the population? | Omitted or misclassified people can change the outcome. |
| Payroll/account data | Which amounts and adjustments belong? | The numerator and denominator must follow plan terms. |
The ACP limits mirror the ADP comparison: the HCE ACP cannot exceed the greater of 125% of the NHCE ACP, or the lesser of 200% of the NHCE ACP and the NHCE ACP plus two percentage points. [1]
Questions for the annual file review
Before approving a report, ask whether the census includes every person required by the document, whether late-year hires and terminated participants were handled consistently, and whether the compensation period matches the stated rule. Ask the administrator to identify assumptions rather than hiding them inside a calculation. A short written exception log makes it easier to distinguish a genuine design issue from a data-cleanup task.
Also separate information gathering from remedy selection. The right response to an incomplete roster is to complete and validate the roster; the right response to a failed calculation may involve a document-driven correction analysis. Conflating those steps can create unnecessary participant disruption and make the audit trail harder to explain later.
Implement a sponsor workflow
Map every contribution code before year-end; identify whether it is an elective deferral, match, after-tax contribution, or another source under the document. Confirm eligible employees and compensation definitions with the recordkeeper or TPA. [1]
- Assign ownership. Name a sponsor-side contact for HR, payroll, finance, ownership, and the recordkeeper file.
- Freeze and reconcile inputs. Save the original extracts, compare them to the document, and log exceptions.
- Review the result. Ask for the population, formulas, assumptions, and any adjustments—not just a pass/fail status.
- Document the decision. Retain approvals, correction calculations, deposits or distributions, and participant communications where applicable.
- Set scope: define the requirement, scope, timing, and decision owner.
- Check evidence: check documents, reports, controls, and open exceptions.
- Assign action: assign the approved action, deadline, and accountable owner.
- Revisit: revisit evidence, changes, and unresolved exposure.
Practical review table
| Review point | Evidence to retain | Escalate when |
|---|---|---|
| Population | Eligibility and classification roster | Ownership, termination, or related-company facts conflict |
| Amounts | Payroll/account reconciliation and code map | Compensation or source treatment is unclear |
| Result | Administrator report and sponsor sign-off | The document, method, or correction route is uncertain |
Review and improve
A durable workflow keeps a contribution-code map, a monthly exception report, and a final review of vesting treatment for any matching contribution affected by a correction. [1]
Use the post-cycle review to convert exceptions into controls. For example, an ownership-information gap can become a quarterly questionnaire; a contribution-code problem can become a payroll change-control test; and a late eligibility feed can become a checklist with a named deadline. Controls should be simple enough that the responsible team can actually perform and evidence them.
Close the loop with a short sponsor meeting after the administrator completes the work. Review what changed from the initial census, who approved each exception, and whether the result triggered a funding, distribution, notice, or design discussion. Store the final report alongside the source extracts and approval notes. That package gives next year’s team a starting point and helps prevent informal knowledge from disappearing when roles change.
For recurring issues, identify a leading indicator rather than waiting for an annual surprise. Examples include a monthly list of new owners and related entities, a payroll-code change report, an eligibility reconciliation, or a balance-adjustment queue. The measure should lead to a specific person reviewing a specific file by a specific date.
Editorial disclaimer: This article is educational and does not provide legal, tax, actuarial, investment, or compliance advice. Retirement plan outcomes depend on the plan document, facts, timing, and applicable law. Work with qualified plan, legal, tax, and payroll advisers before implementing a correction, contribution, or design change.
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Takeaway
The practical takeaway: treat acp testing as a disciplined data-and-document process. Start with the governing terms, validate the population and amounts, preserve the calculation trail, and obtain professional review when facts or correction choices are uncertain.
References
- [1] Internal Revenue Service. ACP Testing Explained supporting guidance. https://www.irs.gov/retirement-plans/401k-plan-fix-it-guide-the-plan-failed-the-401k-adp-and-acp-nondiscrimination-tests