Gestational Age Calculator
NICU staff, neonatologists, and developmental pediatricians use this to figure out post-menstrual age (PMA), corrected gestational age, and chronological age for preemies. Plug in the gestational age at birth and the dates — we'll handle the math that accounts for weeks of prematurity.
NICU Age Details
NICU Age Results
Post-Menstrual Age (PMA)
Corrected Gestational Age
Chronological Age
Weeks of Prematurity
Corrected Age (for follow-up)
Enter gestational age and dates to calculate PMA
NICU Standard
Follows AAP guidelines
PMA + Corrected Age
Dual output format
HIPAA Friendly
No data transmission
Print Reports
Clinical documentation
Note for Neonatal Care Providers
This tool calculates PMA per AAP guidelines — gestational age plus chronological age. For post-discharge developmental follow-up, switch to our corrected age calculator which subtracts weeks of prematurity. Document both numbers in the chart — it matters for continuity of care.
What Is Post-Menstrual Age (PMA)?
Post-menstrual age (PMA) tells you the total developmental time from the first day of mom's last menstrual period to now. You get it by adding gestational age at birth to chronological age since birth. Every NICU uses this number.
Quick example: baby born at 32 weeks, now 4 weeks old chronologically. PMA = 36 weeks. At 8 weeks old, PMA hits 40 weeks — that is full-term equivalence. Simple enough once you have done it a few times.
The PMA Formula
The PMA formula could not be simpler:
Gestational age usually comes from that first-trimester ultrasound — it is the most reliable. No ultrasound? Then you use the first day of the last menstrual period (LMP). It's less precise but it works.
Corrected Gestational Age
Corrected gestational age and PMA are basically the same thing — lots of people in NICU settings use the terms interchangeably. Both mean gestational age plus chronological age. "Corrected" just highlights that you're adjusting for the preterm birth.
That said, some folks make a distinction: PMA (in weeks) for the NICU stay, and "corrected age" (in months) for post-discharge follow-up appointments. Both calculations are identical — it is really just about what unit you express it in.
How NICUs Actually Use These Numbers
Accurate gestational age calculation drives pretty much everything in the NICU. Here is where it shows up:
- Feeding: When to start enteral feeds, how fast to advance, when to fortify — all PMA-driven decisions.
- Respiratory: Weaning from the vent, timing the CPAP trial — correlated with PMA, not just chronological age.
- Vaccines: Most immunizations go by PMA milestones, not calendar age.
- Developmental exams: Dubowitz and other neonatal assessments reference PMA.
- ROP screening: Retinopathy screening schedules are strictly PMA-based.
- Going home: Lots of NICUs want a minimum PMA before they'll even talk discharge.
Prematurity Categories by Gestational Age
| Category | Gestational Age | Risk Level |
|---|---|---|
| Extremely Preterm | < 28 weeks | Very High |
| Very Preterm | 28 to 32 weeks | High |
| Moderate Preterm | 32 to 34 weeks | Moderate |
| Late Preterm | 34 to 37 weeks | Lower |
| Full Term | 37 to 42 weeks | Baseline |
Let's Walk Through One
Baby born March 15, 2025, at 30 weeks gestation. Today is June 3, 2025. Chronological age is 11 weeks 5 days, or about 11.7 weeks. PMA = 30 + 11.7 = 41.7 weeks. This little one has passed term equivalence and is running about 1.7 weeks post-term by PMA. That is the number the team will use for clinical decisions.