What Are CPT Codes in Medical Billing

By Gimbl Clinical Content Team · Healthcare RCM Content Author

Last updated: July 25, 2026

CPT codes tell a payer what a practice did. Here is what they are, the three categories, how they differ from ICD-10 and HCPCS, and how they drive payment.

CPT codes are the five-character Current Procedural Terminology codes, maintained by the American Medical Association, that a practice reports on a claim to tell a payer which medical services and procedures were performed. Each code maps to a specific service, and payers use it, alongside the diagnosis code, to decide how the claim is paid.

What CPT codes are

CPT stands for Current Procedural Terminology, a code set created and maintained by the American Medical Association. Each code is five characters and stands for a specific service, from an office visit to a surgical procedure to a diagnostic test. When a practice submits a claim, the CPT codes are how it tells the insurance payer exactly what was done during the visit.

The three categories of CPT codes

Category I codes are the main set, the five-digit numeric codes for procedures and services that are widely performed, such as an office visit or an eye exam. Category II codes are optional tracking codes for performance measurement and end in the letter F. Category III codes are temporary codes for new and emerging technology and end in the letter T. Most day-to-day billing uses Category I.

How CPT differs from ICD-10 and HCPCS

These three code sets work together on a claim but answer different questions. CPT says what service was performed. The ICD-10 diagnosis code says why it was done. HCPCS Level II codes, which start with a letter, cover supplies, materials, and drugs that CPT does not, such as the V codes for glasses and contact lenses. A clean claim pairs the right CPT code with a supporting diagnosis.

How CPT codes drive payment

Payers attach a value to each CPT code through a fee schedule, so the codes on a claim largely determine what a practice is paid. This is why coding accuracy matters: the wrong code, or a code that the diagnosis does not support, leads to a denial or a reduced payment. The code has to match both the service performed and the documentation in the chart.

CPT codes in eye care

Eye care uses the same CPT system, with the 92000 series for ophthalmological exams and the 99000 E/M codes for medical visits. What makes eye care distinct is that the same CPT code can bill to a vision plan or to a medical carrier depending on the diagnosis, which is a routing decision made at check-in. The full breakdown is in the vision billing codes guide.

Educational information for billing staff and practice owners. Verify current CPT descriptors and payer policy each plan year against primary sources including the AMA and AAPC.