GY, GA, and GZ Modifiers: What Each One Costs You

One of these modifiers means your client can be billed. Another means you've already written the session off and can't bill anyone. Most practices can't tell you which is which.

The GY, GA, and GZ modifiers are how you tell Medicare what you knew before the session started, and who should pay if the claim denies. Get them backward and you either leave money on the table or hand it back.

This matters more than it used to. Marriage and family therapists and mental health counselors have only been able to bill Medicare since January 1, 2024, so plenty of practices are meeting these modifiers for the first time.¹ And nearly every guide explains them with shower chairs and eyeglasses, which isn't much help when you're looking at a psychotherapy claim.

Here's what each one means, the two questions that pick the right one, and where the decision actually gets made.

What the GY, GA, and GZ Modifiers Actually Mean

All three tell Medicare the same basic thing: you already expect this claim to deny. They differ on why you expect it, and on who ends up holding the bill. That second part is the whole ballgame.

The GA modifier means "waiver of liability statement issued as required by payer policy, individual case."² In plain terms: you expected a medical necessity denial, and you have a signed Advance Beneficiary Notice of Noncoverage (ABN) on file. Medicare assigns the denial to your client, so you may bill them. You don't send the ABN with the claim, but keep it. You have to produce it on request.

The GY modifier means "item or service statutorily excluded, does not meet the definition of any Medicare benefit."³ Medicare never covers this, full stop. No ABN is required, and the claim denies whether or not you use the modifier. Your client is liable. So why bother? Because GY generates a clean denial you can forward to a secondary payer.

The GZ modifier means you expected a medical necessity denial and you didn't get an ABN. Medicare automatically denies these lines as provider-liable, with no medical review at all.⁴ You cannot bill your client. GZ isn't a warning label. It's a confession.

Modifier	What it says	Who can be billed
GA	Denial expected, ABN signed	Your client
GY	Never a Medicare benefit	Your client
GZ	Denial expected, no ABN	Nobody. You absorb it.

One hard rule: never put any combination of GA, GY, and GZ on the same claim line.² GA and GZ are opposites by definition. You either got the signature or you didn't.

The Two Questions That Pick Your Modifier

You don't need to memorize this. You need to ask two questions in order.

Question 1: Is this service ever a Medicare benefit?

If the answer is no, it's a statutory exclusion, and you're looking at GY. An ABN isn't required here, though offering one is a courtesy.⁵

Question 2: If it is a benefit, do you expect it to be denied as not reasonable and necessary?

If yes, everything comes down to one thing: did you get a signed ABN before the session? Yes, use GA. No, use GZ, and the write-off is yours.

The distinction that trips people up is that "Medicare won't pay for this" feels like one category. It's two, and they carry opposite paperwork. Statutory exclusion needs no ABN. Medical necessity needs a mandatory one.

Couples counseling shows the fork clearly. When the work is medically necessary treatment of an identified client's diagnosed condition, it's a covered benefit, and you're in Question 2 territory. When it's general marital enrichment with no diagnosis being treated, it isn't a Medicare benefit at all, and you're in Question 1 territory. Same two people on the couch, different answer. The rules around family therapy billing reward practices that can tell those sessions apart on the front end.

The ABN Decision Happens Before the Session, Not in Your Billing Software

Here's the part nobody tells you. By the time a biller is choosing between GA and GZ, the outcome is already locked in. The fork was the signature you did or didn't collect, days earlier. This is a front-desk process problem wearing a coding problem's clothes.

An ABN is mandatory when you expect a medical necessity denial on a service Medicare normally covers. It's voluntary for statutory exclusions, where CMS encourages it anyway so nobody gets surprised.⁵

Timing matters. Deliver the ABN far enough ahead that your client can make a real decision about whether to go forward. Slid across the desk at checkout, it isn't informed consent, and a defective ABN means you can't bill them.

Two things worth checking this week:

• ABNs are Original Medicare only. They do nothing for Medicare Advantage plans, which run their own notice process.⁵ A signed ABN in an Advantage client's chart is false confidence. Verifying which one your client has at intake settles it, and that's exactly what eligibility verification is for.
• Check the date on your form. The revised ABN (Form CMS-R-131) was approved March 13, 2026 and runs through March 31, 2029. The prior version was usable only through May 12, 2026.⁵ If your front desk still prints a PDF someone downloaded in 2023, those signatures may not hold up. An invalid ABN means an unbillable balance. There's an official Spanish version now, too.

Nothing about medicare mental health billing is intuitive, and this is one of the spots where a small habit at the front desk protects real revenue at the back end.

Where Behavioral Health Practices Actually Get This Wrong

Missed appointments don't need a modifier at all. This is the most common mix-up we see, and the most satisfying to clear up. A no-show is a charge for a missed business opportunity, not a charge for a service. So it never goes to Medicare. Don't append GY, don't append GA, don't collect an ABN. Bill your client directly. CMS asks only that your missed-appointment policy apply equally to Medicare and non-Medicare clients.⁶ Practices that route no-shows through Medicare with a modifier attached are doing work nobody asked for, on top of their usual no-show prevention headaches.

The GX modifier rounds out the set: "notice of liability issued, voluntary under payer policy."⁷ It's for voluntary ABNs on statutorily excluded services, and it pairs with GY. Medicare rejects it alongside GA and GZ, which tells you plenty about what it's for.

New Medicare billers inherited none of this. MFTs and MHCs have been able to enroll and bill Part B independently since January 1, 2024, at 75% of the clinical psychologist rate.¹ If you're still working through Medicare enrollment as an LMFT or LPC, build the ABN workflow now, while you're building everything else. One wrinkle to know: services an MFT or MHC furnishes to a hospital inpatient aren't a Part B benefit.¹

A pattern of GZ modifiers is an A/R problem, not a coding quirk. One is a bad day. A pattern means the ABN workflow upstream is broken, and every instance is revenue nobody can recover. That's the kind of trend denial tracking and a monthly A/R audit catch, and a claim-by-claim view never will.

Final Thoughts

These three modifiers aren't really about coding. They're about whether a conversation happened before the session, and who pays when Medicare says no.

That's the takeaway worth keeping: GA means your client can be billed, GY means your client can be billed, and GZ means you absorbed it. The difference is usually one signature, collected days earlier by someone at your front desk.

We work only in behavioral health, so we can tell you what a statutory exclusion looks like in a therapy practice instead of reaching for a shower chair. And your account coordinator is a person who'll help your front desk build the ABN habit, not a ticket queue that explains the GY, GA, and GZ modifiers after the money's gone.

If you're new to Medicare or seeing denials you can't explain, we're glad to look at your A/R with you. Get in touch with BreezyBilling to start a conversation.

Footnotes

1. Marriage and Family Therapists & Mental Health Counselors — Centers for Medicare & Medicaid Services, 2024

2. Modifier GA — Noridian Healthcare Solutions (Medicare Administrative Contractor), 2025

3. Modifier GY — Noridian Healthcare Solutions (Medicare Administrative Contractor), 2025

4. CMS Manual System, Transmittal 2148: Auto Denial of Claims Submitted with a GZ Modifier — Centers for Medicare & Medicaid Services, 2011

5. FFS Advance Beneficiary Notice of Noncoverage (ABN), Form CMS-R-131 — Centers for Medicare & Medicaid Services, 2026

6. Charges for Missed Appointments, Transmittal 1279 — Centers for Medicare & Medicaid Services

7. Modifier GX — Noridian Healthcare Solutions (Medicare Administrative Contractor), 2025