CPT Code 99355: The Definitive Guide [+Reimbursement Rates]

CPT Code 99355 is a prolonged service CPT code add-on.  99355 cannot be billed alone and must be billed with an appropriate procedure code as well as another prolonged service code, 99354.

Add-on Code 99355 fits into a sub-group of add-ons from 99354-99359 of prolonged services codes.  Up until recently, only medical doctors could bill this code with E/M codes but in the last few years many insurance companies have begun to reimburse for it with routine service codes.

This means many Licensed Clinical Social Workers (LCSW), Licensed Professional Counselors (LPC), Licensed Marriage Family Therapist (LMFT), clinical psychologists and psychiatrists can get reimbursed for claims appropriately billed with 99355.

Despite this, many mental health professionals are unaware of this modifier when they could be reimbursed for their extended sessions!

CPT Code 99355 Definition

99355 is defined as an add-on code used to report an additional 30 minutes beyond the first hour of therapy. This means 99355 must be billed with another procedure code.

CPT Code 99355 Reimbursement Rate

99355 reimbursement rate99355 is not universally reimbursed and depends on the provider’s credentials and the insurance plan. When it is allowed, the fee schedule often allows for reimbursement beneath 99354, which involves a greater amount of time.

CPT Code 99355 Reimbursement Rate (Medicare 2020):  $100.33


In our experience, the fee schedule puts it in a similar price range 90834. It is always best to call the insurance ahead of time to make sure it is covered. Our billing service can do this for you.

CPT Code 99355 Time Length

For mental health professionals, the 99355 is almost always billed with 90837 or 90847. In addition, the first amount of extra time must be billed with 99354. Only if both 90837/90847 and 99354 have been appropriately billed can the extra time be billed with 99355.

In addition, 99355 can be billed multiple times for each additional 30 minute interval.

Individual Psychotherapy

  • 53-89 minute session – 90837.
  • 90-134 minute session – 90837 + 99354.
  • 135-164 minute session – 90837 + 99354 + 99355.
  • 165-194 minute session – 90837 + 99354 + 99355 + 99355.

Group Psychotherapy w/Patient Present

  • 26-79 minute session – 90847.
  • 80-124 minute session – 90847 + 99354.
  • 125-154 minute session – 90837 + 99354 + 99355.
  • 155-184 minute session – 90837 + 99354 + 99355 + 99355.

99355 vs. 99354

99355 cannot be billed without 99354. In the case of extended sessions, you would bill 99355 as well. Until the sessions reach an appropriate length you cannot bill 99355. Make sure to document the time spent to ensure you can bill 99355.Billing CPT Code 99355

99355 License Level Requirements

Make sure you meet these mental health license level requirements before billing services with CPT Code 99355:

  • Licensed Clinical Social Workers (LCSW)
  • Licensed Professional Counselors (LPC)
  • Licensed Marriage Family Therapist (LMFT)
  • Licensed Clinical Psychologists (PsyD or PhD)
  • Psychiatrists (MD)

CPT Code 99355 Can Be Billed Multiple Times

Unlike 99354, 99355 can be billed multiple times. While the reimbursement varies significantly (some may limit it to a certain number of times) if the session is several hours then 99355 can be billed multiple times!

99355 Billing Restrictions

Even though 99355 can now be billed by non-medical personnel it does not mean it is universally accepted.If you bill with us, we can call on your behalf to find out before you have an extended session.

While 90837 and 90847 are typically allowed, 90846 is rarely allowed to be billed with prolonged service codes.

How Do I Bill CPT 99355?

Just like other CPT codes, the procedure code 99355 should go in the 24(c) location of a CMS 1500. Since it is an add-on it must be billed with 90837 or 90847 as well as 99354 make sure you include those procedure codes on a separate line in section 24.

CMS 1500 with CPT Code 99355


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