How to Resolve an ACA Marketplace Data Matching Issue (DMI) in 2026: Documents, Deadlines, and Keeping Your Subsidy

You finished your Marketplace application, picked a Silver plan, and started paying premiums. A few weeks later a letter shows up — or a notice flashes in your HealthCare.gov account — telling you the Marketplace needs more information to verify your application. You have 90 days to send documents. The notice mentions losing your subsidy, losing your coverage, and a number of acronyms you didn't sign up to learn.

This is a data matching issue, or DMI. It is not an accusation, it is not a tax audit, and it does not mean you did anything wrong. It means the Marketplace ran a database check on your application — against IRS records, Social Security, the Department of Homeland Security — and the answers didn't perfectly match what you reported. The fix is paperwork. The risk, in 2026, is that the rules tightened in August 2025 and a lot more applications now get flagged than did a year ago.

Here is the practical playbook: what the most common DMI types are, exactly which documents resolve each one, the upload process, the new self-attestation rules, and the five mistakes that turn a routine paperwork issue into a lost subsidy.

The Marketplace verifies application answers against approved electronic data sources. Most applications match cleanly and you never hear about it. When the system can't confirm something, it creates an inconsistency and asks for documentation. There are roughly seven categories of DMI:

• Income (annual household). By far the most common. Your projected 2026 income doesn't match IRS records from your most recent return.
• Income (current/monthly). Used when you applied for Medicaid eligibility or are near the FPL threshold and need to verify current monthly income.
• Citizenship. The SSA can't confirm you're a U.S. citizen based on what you entered.
• Immigration status. DHS can't verify the document number you provided.
• Social Security number. The SSN you entered doesn't match SSA records for the name and date of birth you gave.
• American Indian or Alaska Native status. Required to access the cost-sharing reduction (CSR) for AIAN consumers.
• Incarceration status. Required because incarcerated individuals are not eligible for Marketplace coverage.

Income DMIs make up the lion's share — and a new rule expanded how many income DMIs the Marketplace generates.

Before August 25, 2025, applicants could "self-attest" their income in many situations — sign under penalty of perjury that the number was accurate and proceed to enrollment with subsidies. As part of the 2025 Final Marketplace Integrity Rule, CMS narrowed the self-attestation policy. Two newly-triggered DMI situations:

1. No tax data on file. If the IRS has no recent return for you — common for new filers, recent immigrants, returning expats, very-low-income filers below the threshold — the Marketplace can no longer accept self-attestation. You get an income DMI automatically.
2. Projected income above 100 percent FPL, data shows below. If you project an income that qualifies you for marketplace subsidies, but federal data shows you actually earned below the FPL last year (and therefore would have been Medicaid-eligible), you get a DMI to back up the projection.

The 90-day income DMI rules are scheduled to sunset on December 31, 2026 without further action. That means if your DMI is open going into 2027, the resolution timeline may change. The cleanest move is to clear the inconsistency well before the end of 2026.

Income DMI

The Marketplace asks for documentation that backs up your projected annual household income. Acceptable documents, ranked roughly by how cleanly they resolve the issue:

• Most recent federal tax return (Form 1040 with all schedules). Best evidence if last year's income is similar to your projection.
• W-2s for the current or prior year. Good supporting evidence; pair with a brief explanation if projection differs from last year.
• Recent pay stubs (typically four most recent). Strongest for current-year income; annualize and explain the math.
• Signed letter from employer. Use when you're newly hired and don't yet have four pay stubs. Must state job title, gross pay, pay frequency, and date of hire.
• Self-employment records. Profit-and-loss statement plus most recent Schedule SE. Add a one-page narrative if income is variable.
• Social Security benefit award letter. For SSA, SSDI, or SSI income; the most recent COLA letter works.
• Unemployment award letter or weekly benefit notice.
• Pension or retirement account distribution statements.
• Court orders for alimony.

If your projected income is materially different from last year's tax return — for example, you took a pay cut, started a new business, retired early, lost a job — include a one-page signed letter explaining the change in plain language. The Marketplace reviewer reads both the documents and the narrative.

Citizenship DMI

The SSA generally confirms citizenship when your SSN matches your application, so a citizenship DMI is usually solved by uploading proof of citizenship directly:

• U.S. passport (current or expired within five years)
• Certificate of Naturalization (Form N-550 or N-570)
• Certificate of Citizenship (Form N-560 or N-561)
• State-issued enhanced ID
• U.S. birth certificate plus a current photo ID (driver's license or state ID)
• Consular Report of Birth Abroad (for those born to U.S. citizens overseas)

Immigration Status DMI

Upload a copy of the immigration document whose number you entered on the application — green card (I-551), employment authorization document (I-766), I-94 arrival/departure record, asylum approval letter, or refugee admission letter. The Marketplace checks the document number against DHS, so the cleanest fix is uploading the actual document so a reviewer can manually verify.

Social Security Number DMI

Usually a typo. Open your application, fix the SSN, and the inconsistency clears automatically after the next data sync — no document needed. If the SSN is correct as entered, upload the Social Security card itself.

1. Log into your account at HealthCare.gov.
2. Click your name in the upper-right corner and select My applications and coverage.
3. Open the application that has the inconsistency (it will be flagged with a banner).
4. On the Application details tab, find the section listing open inconsistencies. Click the type you want to resolve.
5. Choose the document type from the dropdown menu. Match it to what you're uploading — e.g., "Tax return" if you're sending a 1040.
6. Click Select file(s) and pick your document from your computer.
7. Click Submit.

Acceptable formats: PDF, JPG, JPEG, PNG, BMP, GIF, TIFF. Maximum 10 MB per file. If your document is larger, split it or compress; if it's multiple pages, combine into one PDF when possible. Within a few weeks you'll get a notice — either confirming the issue is cleared, asking for additional documents, or stating the issue is closed without resolution.

If You Can't Upload

Each notice includes a mailing address for paper submission. Mail is materially slower — four to six weeks longer on average. Always send copies (never originals) via tracked mail, write your application ID and DMI type on each page, and keep the tracking number. If the document is sensitive — like a passport or immigration record — uploading the digital scan is both faster and safer than mailing the original.

Uploading on Day 85 is technically within the deadline but offers no margin if your first document is rejected. Treat 30 days as your personal cap.

1. Ignoring the notice because the plan is still active

The Marketplace keeps you enrolled with subsidies during the resolution window — so the bill at the doctor's office still shows your insurance, and the premium doesn't change. People interpret this as "everything is fine." It is not. On day 91, APTC adjusts, premiums spike, and reconciliation at tax time can cost thousands.

2. Uploading the wrong document type

For an income DMI, uploading your driver's license does nothing — it's not income evidence. The dropdown matters. If you upload a tax return, choose "Tax return" from the menu, not "Other." Mismatched documents are often filed without notice that the issue isn't resolving.

3. Uploading a document with missing pages

A 1040 without the Schedule 1 attached, a W-2 with the bottom cut off, pay stubs missing year-to-date totals — these get rejected. PDFs of complete documents are cleaner than phone photos of partial pages.

4. Lowering income to "match" the database

Don't change your projection to mirror last year's tax return unless your actual projected income matches. The IRS reconciles on Form 8962 anyway. A projection that is too low triggers a clawback at tax time when your actual income comes in higher — and starting in 2026, the APTC repayment cap is gone. Every overpaid dollar comes back, regardless of how much you owe.

5. Missing a request for additional documents

Reviewers sometimes accept the first document but ask for one more. The follow-up notice goes to the same address and account banner as the initial DMI. People who resolved the first request stop checking. Set a calendar reminder for 30 days after upload to check your account status.

If your 90 days expired and APTC was adjusted or coverage ended:

1. You can still submit documents. The Marketplace will review them and, if accepted, may reinstate eligibility prospectively. Past months without subsidy generally are not refunded retroactively.
2. Contact the Marketplace Call Center (1-800-318-2596). If you have a reasonable explanation for missing the deadline — illness, family emergency, mail problem, language access — request a reconsideration. There is no formal appeal for missing a DMI deadline, but reviewers have discretion in limited cases.
3. Check whether you qualify for a Special Enrollment Period. Losing minimum essential coverage due to a DMI denial does not automatically trigger an SEP, but related life events (a move, a marriage, a job change) might let you re-enroll.
4. File on time. Even if your APTC was adjusted, you still file taxes normally. The reconciliation on Form 8962 captures what you actually were eligible for during the year.

A Marketplace DMI is a paperwork problem with a fixed deadline. The Marketplace asks; you upload; a reviewer confirms. The process becomes a subsidy-loss problem only when people wait, upload the wrong document, or ignore a follow-up request. In 2026, more applications get flagged than before — the August 2025 self-attestation rule change moved the line — so a notice this year does not mean your application is wrong, only that the data sources didn't line up automatically.

Five-minute version: open the notice, read which DMI type was triggered, gather the documents listed above for that type, log in and upload through the Application details tab within 30 days, then check your account again 30 days later to confirm resolution or respond to a follow-up. Don't change your income projection to match a database. Don't mail documents unless upload is impossible. And don't ignore the notice just because your coverage still works in the meantime.