ACA Filing Errors That Trigger IRS Penalties — and How to Catch Them Early

The Five Error Types That Drive ACA Penalties — and Why Most Are Preventable

ACA filing errors fall into five predictable categories. Most of them are not failures of intent — they are failures of process, configuration, and review. The coverage was offered. The forms were generated. The vendor submitted the file. The problem is in what the forms actually said, how the headcount was calculated, or whether the transmission was verified.

The most expensive thing about these errors is not that they are hard to prevent. It is that they are easy to miss during filing season and show up — with interest compounded across months, employees, and years — on IRS Letter 226-J.

1095-C Offer and Coverage Errors

Wrong Line 14 Code

Line 14 tells the IRS what coverage was offered — or not offered — for each month. The most common wrong Line 14 codes are 1H (no offer) when coverage was actually offered, or 1E when the actual offer was more limited in scope. A wrong Line 14 code means nothing else on the form matters — the IRS reads no offer.

Inconsistent Offer-and-Coverage Codes for Enrolled Employees

Code 2C on Line 16 means the employee was enrolled in coverage for the month. If an employee is coded 2C but their Line 14 code doesn't reflect a valid coverage offer, the IRS data is internally inconsistent.

Failure to Report Dependent Coverage Correctly

Code 1E on Line 14 represents an offer to the employee, the employee's spouse, and dependents. Code 1B represents an offer only to the employee. An employer that offered employee-only coverage but coded 1E has misrepresented its offer.

Affordability and Safe Harbor Errors

Wrong Line 15 Amount

Line 15 is supposed to carry the lowest-cost self-only minimum-value monthly premium available to the employee — not what the employee elected, not the family contribution. As explained in our ACA Affordability Safe Harbors article, the Line 15 amount is what the IRS uses to evaluate affordability when no safe harbor code is present.

Missing or Wrong Line 16 Safe Harbor Code

Line 16 is where the employer communicates its affordability defense. A blank Line 16 — when a valid safe harbor applies — tells the IRS that no affordability defense exists for that employee-month.

Headcount and Eligibility Errors

Variable-Hour and Seasonal Employee Misclassification

Variable-hour, seasonal, and part-time workers must be tracked through an ACA measurement period before eligibility can be determined. If that employee eventually receives a premium tax credit, the absence of a measurement period means the employer cannot document why the employee was not offered coverage.

Waiting Period Errors

The ACA's 90-day waiting period limit permits a limited non-assessment period before coverage must be offered to a newly eligible full-time employee. Employer HR and payroll systems frequently implement waiting periods in ways that exceed the 90-day limit.

Form 1094-C Column (b) Headcount Errors

Form 1094-C Part III, Column (b) is the monthly full-time employee count. The IRS uses this count as the base for the 4980H(a) penalty formula. An inflated headcount — because headcount was pulled from payroll totals rather than measured by hours of service — inflates the 4980H(a) penalty calculation directly.

Filing and Transmission Errors

Accepted with Errors Left Uncorrected

AIR accepts files with individual record errors through the "Accepted with Errors" status. A filing that stays in "Accepted with Errors" status without the errors being corrected is not a complete ACA filing. Our ACA Filing Transmission article explains the full AIR filing lifecycle and where silent failures occur.

AATS Testing Accepted, Production Filing Missing

The IRS Assurance Testing System (AATS) is a pre-production testing environment. A file accepted in AATS is not a filed return and creates no IRS filing record.

Incorrect FEIN or Mismatched EIN

Filing under a different EIN means the filing may not be matched to the ALE at issue. The IRS may treat the employer as a non-filer even if a technically accurate return exists somewhere in the system.

Multi-Year Errors That Compound Faster Than Employers Expect

The most expensive ACA errors are the ones no one catches for multiple years. A variable-hour misclassification decision made once runs unchanged for three filing years and produces three years of ESRP exposure.

As covered in our ACA Penalty Calculator article, ESRP exposure compounds multiplicatively — employee count, multiplied by months, multiplied by years. An error affecting 20 employees across three years is 720 assessable employee-months.

What Early Detection Actually Requires

Early detection is not an audit activity. It is a production control that runs during filing season — before the employer clicks submit. What makes early detection real is a comparison: does the data in the generated forms match the employer's actual compliance position?

The Three Operational Controls That Catch Most ACA Errors Early

Control 1 — The Pre-Transmission Line 14/15/16 Population Audit

Before the filing is transmitted, run a frequency distribution of Line 14, 15, and 16 codes across the employee population. This catches systematic errors immediately: a Line 14 code of 1H applied to employees who were enrolled; a Line 15 with the family contribution amount; a missing Line 16 safe harbor code on an entire employee class.

Control 2 — The Offer-to-Eligibility Reconciliation

Compare the employer's internal eligibility roster against the 1095-C population. Any employee in the eligibility roster who is coded 1H (no offer) on their 1095-C is a potential problem. Any employee not in the eligibility roster who is coded with an offer code is a different kind of problem.

Control 3 — The Affordability Math Verification

Before filing, run the safe harbor calculation for each employee class and verify: (a) the Line 15 amount matches the lowest-cost self-only minimum-value premium for that class; (b) the Line 16 safe harbor code matches the safe harbor actually applied; and (c) the safe harbor math passes using the current year's indexed affordability percentage.

Key Takeaways