What Is CPT Code 99391?
CPT 99391 is a preventive medicine code that reports a comprehensive well-child visit for an established infant under one year of age. It covers the age-appropriate history, exam, and anticipatory guidance a pediatrician delivers at each well-baby check. Code choice depends on the child’s age and whether the patient is new or established, not on time or medical decision-making.
Established infants only. 99391 is for a patient the practice has seen before. A truly new infant uses 99381, which pays more, so getting the status right protects revenue.
Age-driven, not time-driven. The code is selected by the patient’s age on the visit date, so a baby who turns one moves to 99392, not 99391.
Same-day services need modifier 25. When vaccines or a separate sick problem are handled at the same visit, modifier 25 is what keeps both services payable.
What Does CPT 99391 Cover?
CPT 99391 covers a periodic, comprehensive preventive visit for an established infant under one year: a full age-appropriate history, a head-to-toe exam, growth and development assessment, anticipatory guidance for parents, and the ordering of any needed labs or screenings. It is the routine well-baby checkup, not a sick visit, and payers cover it as preventive care.
The preventive medicine codes are unusual because they are not scored on time or medical decision-making the way office E/M codes are. Selection turns on two facts: the patient’s age on the date of service and whether the patient is new or established. The American Academy of Pediatrics ties these visits to its Bright Futures periodicity schedule, which sets well-visit checkpoints at birth, 3 to 5 days, by one month, and again at 2, 4, 6, and 9 months, so a single healthy infant generates several 99391 claims in one year. The CY 2026 Physician Fee Schedule (CMS-1832-F) left the well-child codes stable in the relative value set and set the non-qualifying conversion factor at $33.42, but infants are billed under commercial and Medicaid rates that each payer sets independently.
What Is the Difference Between 99391 and 99381?
99391 is for an established infant and 99381 is for a new one. New means the practice has not provided a face-to-face service from a physician of the same specialty in the same group within the past three years. A prior sick visit inside that window makes the child established, so the well visit is 99391, even if it is the family’s first physical at your office.
This is the most expensive quiet error in well-child billing, because 99381 carries a higher relative value than 99391 and payers audit for it. If a baby was seen for a fever four months ago and returns for the 6-month checkup, the correct code is 99391, not 99381. Bill 99381 and the claim may pay more today and get clawed back later. The reverse also costs you: coding an established 99391 for a genuinely new patient leaves money on the table. One question we hear constantly from practice managers is why their preventive claims keep getting adjusted after payment, and the answer is almost always a new-versus-established mismatch that the payer caught on post-payment review.
| Age on date of service | New patient | Established patient |
|---|---|---|
| Infant, under 1 year | 99381 | 99391 |
| Early childhood, 1 to 4 | 99382 | 99392 |
| Late childhood, 5 to 11 | 99383 | 99393 |
| Adolescent, 12 to 17 | 99384 | 99394 |
| Young adult, 18 to 39 | 99385 | 99395 |
Which ICD-10 Codes Pair With 99391?
Pair 99391 with Z00.129 when the well exam shows no abnormal findings, or Z00.121 when it does, adding a code for the finding itself. For the newborn period, use Z00.110 for an exam under 8 days old and Z00.111 for 8 to 28 days. The diagnosis must match what the note actually documents.
Diagnosis choice is a common audit trigger because it is easy to default to one Z code for every baby. If the note documents an abnormal finding, Z00.129 is wrong; use Z00.121 and append the specific diagnosis. If nothing abnormal is found, Z00.121 overstates the visit. In our experience matching providers with billing partners, this mismatch is one of the top three reasons well-visit claims get flagged on post-payment audit.
| Situation | ICD-10 code | Notes |
|---|---|---|
| Well exam, no abnormal findings | Z00.129 | Most common primary diagnosis |
| Well exam, abnormal finding | Z00.121 | Add a code for the finding |
| Newborn exam, under 8 days | Z00.110 | Newborn period |
| Newborn exam, 8 to 28 days | Z00.111 | Newborn period |
New versus established status, age-band transitions, and diagnosis matching are the small calls that decide whether an infant well visit pays in full or gets clawed back on audit. If your preventive claims are denying or underpaying, a billing partner that specializes in pediatrics can put a pre-submission check behind every 99391. Get matched with vetted medical billing companies, free.
When Do You Add Modifier 25 to 99391?
Add modifier 25 when a second, separately payable service happens at the same visit. There are two common cases: when you also give vaccines, append 25 to the preventive code (99391-25) so it pays alongside the administration codes; when you also treat a separate sick problem, append 25 to the problem E/M, for example 99213-25, not to 99391.
This is where practices lose same-day revenue. Payers bundle a second service into the preventive visit unless modifier 25 signals that the work was significant and separately identifiable. When a well visit includes immunizations, the vaccine administration codes 90460 and 90461 can bundle into the preventive visit, so append modifier 25 to 99391 to keep both paid. When a well visit includes a separate sick problem, report the problem E/M (99212 through 99215) with modifier 25, leave 99391 unmodified, and link the acute diagnosis to the E/M. Across the billing companies we vet, the modifier 25 placement error is the single most common revenue leak on same-day pediatric claims.
| Same-day scenario | Modifier 25 goes on | Example |
|---|---|---|
| Well visit + vaccines | The preventive code | 99391-25 + 90460 + 90461 |
| Well visit + separate sick problem | The problem E/M | 99391 + 99213-25 |
| Well visit + trivial finding only | Neither, no separate E/M | 99391 alone |
What Services Can You Bill Alongside 99391?
Several routine well-baby services are separately payable on top of 99391: vaccine administration (90460 and 90461), developmental screening (96110), emotional or behavioral screening (96127), and vision screening (99173). Each needs its own documentation, and each is money left behind when it gets bundled into the visit by default.
The well visit payment does not include these add-ons, so billing them is not upcoding, it is accurate charge capture. Developmental screening with a standardized tool such as the Ages and Stages Questionnaire or M-CHAT is reported with 96110 and requires the tool name, the score, and the clinician’s interpretation in the note, or payers deny it. When vaccines are given, remember the two-part rule: bill both the product code and the administration code, and count components for 90460 and 90461. Missing any of these lines is the difference between a fully captured well visit and one that quietly underpays. For practices new to pediatric billing workflows, our guide on understanding the basics for new practices covers the foundational charge capture steps.
How Do You Prevent the Most Common 99391 Denials?
Most 99391 denials come from a wrong patient status, an age-band mismatch, a missing modifier 25, or a diagnosis that does not match the note. Every one is preventable before the claim goes out.
- Verify new versus established first. Check the three-year, same-group, same-specialty history before choosing 99391 over 99381.
- Match the code to the age on the service date. Move to 99392 the moment the infant turns one, even by a single day.
- Add modifier 25 to the right code. Put 25 on 99391 when vaccines are given, and on the problem E/M when a separate sick issue is treated.
- Choose the diagnosis the note supports. Use Z00.129 for a clean exam and Z00.121 plus a finding code when something abnormal is documented.
- Capture every add-on service. Bill 96110, 96127, 99173, and the vaccine codes separately rather than folding them into the visit.
- Document screenings completely. Record the tool, score, and interpretation for any developmental or behavioral screen.
- Keep two separate notes for same-day problems. Support the sick E/M with its own history, exam, and plan, distinct from the preventive service.
What Does One Miscoded Well Visit Cost?
A single miscoded infant well visit can lose $90 or more when a same-day sick service is bundled for a missing modifier 25, and more still when screenings go unbilled. The errors are small on one claim and large across a panel of hundreds of infants seen every year.
Take a 9-month-old established patient in for the routine checkup. The pediatrician documents the full preventive exam (99391, Z00.129), runs a standardized developmental screen (96110), gives the scheduled vaccines with counseling (90460 and 90461 by component), and, after finding iron-deficiency anemia on a hemoglobin screen, separately evaluates it and starts iron drops (99213-25, D50.9). Coded correctly, that is four paid lines: the preventive visit, the screen, the vaccine administration units, and the problem E/M. Drop the modifier 25 and the 99213 bundles into the well visit and pays nothing, a roughly $90 loss on that claim alone. At a representative $160 for the preventive visit and $90 for the problem E/M, careless coding turns a $250-plus encounter into a $160 one. The most common issue we see providers run into is not recognizing this pattern until a full quarter of underpayments has already posted.
Frequently Asked Questions
99391 is for established patients only. An established patient is one seen by a physician of the same specialty in the same group within the past three years. A new infant is billed with 99381 instead, which carries a higher relative value, so confirming patient status protects both accuracy and revenue.
Yes, when the sick problem is significant and separately identifiable from the preventive visit. Report the problem E/M (99212 through 99215) with modifier 25 and link the acute diagnosis to it, leaving 99391 unmodified. The record must document the acute problem as a distinct service with its own history, exam, and plan.
Use Z00.129 for a routine infant exam without abnormal findings and Z00.121, plus a code for the finding, when something abnormal is documented. For a newborn, use Z00.110 under 8 days old or Z00.111 from 8 to 28 days. The diagnosis must match the documentation.
No. Medicare does not cover preventive medicine codes 99391 through 99397 for its own beneficiaries. This rarely affects infants, who are covered by commercial plans or Medicaid. Under the Affordable Care Act, most commercial plans cover Bright Futures well-child visits at no cost-sharing, and Medicaid covers them through the EPSDT benefit.
On the child’s first birthday. The preventive code is chosen by age on the date of service, so a visit on or after the first birthday is 99392, and a visit even one day before is still 99391. Flag charts approaching the first birthday so the front desk catches the transition before the claim goes out.
Often yes. Because vaccine administration codes can bundle into the preventive visit, many payers require modifier 25 on 99391 to pay both. Append 99391-25 alongside the administration codes 90460 and 90461, and always report both the vaccine product code and the administration code.
Next Steps
Billing a new infant? See our guide on CPT 99381 for the new-patient version of the infant well visit.
Toddler aging up? Read our CPT 99392 guide for the early childhood well-visit code that takes over at age one.
New to pediatric billing? Start with our overview on understanding the basics for new practices.
Ready to hand well-visit billing off? Get matched with vetted pediatric billing companies that catch the modifier 25 and status errors before they cost you.
99391 sits at the center of a pediatric preventive workflow full of new-versus-established rules, modifier 25 traps, and separately billable screenings that decide whether your well visits pay in full. If preventive denials or underpayments are draining your revenue, stop guessing and get matched with a billing company that lives in pediatric coding. Pediatrician Billers connects you with vetted partners, with rates starting as low as 6% and no cost to request quotes. More than 2,000 providers matched across all 50 states.
