What Are G-Codes in Medical Billing? - Detailed Explanation

Medical billing is built on codes. They help healthcare providers get reimbursed accurately and allow payers like Medicare to track services. While CPT and ICD codes are common, G-codes play a unique and important role, especially when it comes to Medicare billing.

If you’re a provider, biller, or practice manager working with Medicare patients, understanding G-codes is essential.  These codes are often the key to getting paid for preventive care, chronic condition management, and outpatient services that aren't captured by traditional CPT codes. These codes are just one piece of the broader medical coding framework that includes CPT, ICD, HCPCS, and more.

This guide will walk you through what G-codes are, when to use them, how they differ from CPT codes, and how to make sure your claims get processed correctly.

What Are G-Codes?

G-codes are a special set of Medicare billing codes that fall under HCPCS Level II. They’re used when a service doesn’t have a matching CPT code or when the service is tied to a specific federal or Medicare program. In simple terms, they act as “extra codes” that cover situations not included in standard CPT coding.

These codes:

• Apply only to Medicare patients
• Often represent time-limited, pilot, or preventive services
• Help track services unique to Medicare programs

Every G-code starts with the letter “G” followed by four numbers. For example:

• G0442 - Annual alcohol misuse screening
• G0439 - Subsequent annual wellness visit
• G0463 - Hospital outpatient clinic visit

Think of G-codes as Medicare’s way of filling the gaps in billing when regular CPT codes don’t apply.

Why Medicare Uses G-Codes

Medicare often launches new initiatives before CPT codes are created. Instead of waiting for the American Medical Association to assign a CPT code, CMS creates a G code. These codes can be used immediately and are often later replaced by CPT codes once they become permanent.

Reasons Medicare uses G-codes:

• To track preventive care services
• To measure outcomes for value-based care programs
• To reimburse for telehealth and chronic care services
• To test new programs before rolling them out nationally

Using G-codes helps Medicare collect data, shape policy, and control costs.

Common G-Codes and Their Uses

Here are some of the most commonly used G-codes and where they apply:

G-Code	Description	Use Case
G0402	Initial preventive physical exam (IPPE)	New Medicare patient “Welcome” visit
G0438	Annual wellness visit, first visit	Once-in-a-lifetime after 12 months of Part B
G0439	Annual wellness visit, subsequent	Used every year after the first
G0444	Annual depression screening	Covered once per year
G0101	Pelvic and clinical breast exam	For cervical or vaginal cancer screening
G0463	Outpatient hospital clinic visit	Frequently used in facility billing

What Providers Should Know About G-Codes

G-codes may seem like just another set of billing codes, but for providers working with Medicare patients, they carry a lot of weight. Here are a few key points every provider should keep in mind:

1. G-Codes Are Medicare-Specific

Unlike CPT codes, G-codes only apply to Medicare beneficiaries. If you submit them for non-Medicare patients, the claim will almost always be denied.

2. They Often Change or Expire

Many G-codes are temporary. Medicare creates them for new services, pilot programs, or special reporting needs. Once a permanent CPT or HCPCS code is assigned, the G-code may be deleted. That means providers and billers need to stay updated every year.

3. They’re Tied to Compliance and Quality Programs

Some G-codes are used for MIPS, PQRS, and other CMS quality reporting programs. Failing to use the right code can not only delay payment but may also affect compliance scores and incentives.

4. Documentation Is Critical

Just like CPT or ICD-10 codes, G-codes require solid documentation. If your notes don’t back up the service billed, you risk denials, audits, or even accusations of improper billing.

5. Telehealth Has Expanded Their Use

During COVID-19, CMS introduced new G-codes for telehealth. Many are still active today, making it easier to get reimbursed for virtual visits. Providers offering telehealth should double-check which G-codes apply to their services.

6. They Affect Reimbursement Rates

Because G-codes often represent preventive services, screenings, or new treatments, reimbursement rates can differ from standard CPT codes. Always check the Medicare Fee Schedule for the current rate.

Key Differences Between G-Codes and CPT Codes

Feature	G-Codes	CPT Codes
Maintained By	CMS (Medicare)	AMA
Purpose	Temporary, Medicare-specific services	Broad use across all payers
Use Case	Preventive care, pilot programs, telehealth, value-based care	Most office visits, procedures, and surgeries
Payment Source	Primarily Medicare	Medicare, Medicaid, and Commercial insurers
Flexibility	Created and retired quickly	Updated annu

How to Use G-Codes Correctly

Using G-codes isn't just about choosing the right number. You also need to understand how to use them with modifiers, units, and proper documentation. Here are some best practices:

1. Always Check Medicare Guidelines

CMS outlines specific rules for each G-code, including when it can be billed, what documentation is needed, and whether the patient must meet certain criteria.

For example:

G0439 requires that G0438 has already been performed in a prior year.
G0444 (depression screening) must be 15 minutes and use a standardized tool.

2. Use Modifiers When Needed

Some G-codes require modifiers like:

25 - Significant, separately identifiable E/M service
95 - For synchronous telehealth
GA - Waiver of liability statement on file

3. Track Frequency Limits

Many G-codes are limited to once per year, per provider or per beneficiary. Submitting them too often can result in denials or overpayments.

4. Include Supporting Documentation

Medicare audits often focus on G-code usage. Your documentation should clearly show:

• Time spent
• Tools used (screenings, questionnaires)
• Provider credentials
• Patient consent, when needed

Missing any of these details could risk a post-payment review.

Real-World Example: How G-Codes Come Into Use

Imagine a provider sees a new Medicare patient for a preventive visit. The billing team submits CPT 99385 (new patient preventive exam). A few weeks later, the claim is denied. Why?

Because Medicare doesn’t reimburse CPT 99385 for preventive services. Instead, Medicare uses a G-code: G0402 (Initial Preventive Physical Exam). This service is covered only once in a patient’s lifetime, and it must be done within the first 12 months of enrolling in Medicare.

If the provider had billed G0402 with proper documentation, the claim would have been paid without delay.
This shows exactly how G-codes come into play; they replace CPT codes for certain Medicare-covered services.

How to Stay Updated on G-Codes

G-codes aren’t permanent. Medicare often introduces new ones, updates existing codes, or retires old ones as services evolve. For providers and billing teams, staying current is the only way to avoid denials and compliance issues. Here’s how to keep up:

1. Check CMS Updates Regularly

The Centers for Medicare & Medicaid Services (CMS) publishes coding updates every year, usually in October. This includes new G-codes, deleted codes, and reimbursement changes. Bookmark the CMS website and review the annual updates.

2. Subscribe to Official Bulletins

Sign up for Medicare Learning Network (MLN) newsletters and local Medicare Administrative Contractor (MAC) bulletins. These provide real-time updates on coding and billing changes.

3. Use Updated Coding Software

Good billing or practice management software should update code sets automatically. Make sure your system refreshes ICD, CPT, and HCPCS codes each year so you’re never billing with outdated codes.

4. Provide Ongoing Training for Staff

Coders and billers should receive regular training on Medicare-specific codes, including G-codes. Even experienced staff benefit from refreshers when new rules or services are added.

5. Join Professional Associations

Organizations like AAPC and AHIMA often provide coding updates, webinars, and quick-reference guides. These are great for staying ahead of industry changes.

Conclusion

G-codes are the key to getting paid for services that don’t fall under CPT. Whether it’s a wellness visit, a preventive screening, or a telehealth check-in, the right G-code makes the difference between a clean claim and a denial. The challenge with G-codes is that they change often, expire, or come with specific rules that are easy to miss. Many practices end up losing revenue without realizing it. That’s why it’s so important to keep your team updated on the latest Medicare guidelines and coding changes. 

At OneMed Billing, we keep track of every Medicare update so your team doesn’t have to. Our medical billing coders know how and when to apply G-codes correctly, helping you stay compliant, reduce rework, and protect your revenue.

Frequently Asked Questions (FAQ)

Q1. What are G-codes in medical?

G-codes are Medicare-specific billing codes used for services that don’t have a CPT code, are tied to federal programs, or are temporary for new services.

Q2. Are G-codes still used?

Yes, G-codes are still used by Medicare, especially for preventive services, wellness visits, quality reporting, and certain telehealth services.

Q3. What is the difference between CPT codes and G-codes?

CPT codes are standard codes used by all payers to bill medical services, while G-codes are Medicare-only and often temporary, created for services not yet assigned a CPT code.

Q4. Where can providers find the latest list of G-codes?

Providers can find the latest list of G-codes on the Centers for Medicare & Medicaid Services (CMS) website, specifically in the annual HCPCS Level II code updates.