Calculate your premature baby's adjusted age by subtracting weeks born early from chronological age. Free preemie age tool.
Premature babies are assessed using adjusted age (also called corrected age) rather than chronological age when tracking developmental milestones. Adjusted age accounts for the weeks your baby was born early, giving a more accurate picture of where they should be developmentally.
For example, a baby born at 32 weeks gestation (8 weeks early) who is now 6 months old chronologically has an adjusted age of about 4 months. Pediatricians use this adjusted age to set realistic expectations for milestones like rolling, sitting, and walking.
Most doctors recommend using adjusted age for milestone tracking until your child is 2-3 years old, at which point most preemies have caught up to their full-term peers. This calculator helps you quickly determine your baby's adjusted age from their birth date and weeks of prematurity. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
Using chronological age for a preemie can cause unnecessary worry about delayed milestones. Adjusted age provides a fair comparison to full-term peers and helps pediatricians make accurate developmental assessments. This calculator removes the guesswork so you can track your preemie's progress with confidence. Having a precise figure at your fingertips empowers better planning and more confident decisions.
Chronological Age (weeks) = (Today − Birth Date) / 7 Adjusted Age (weeks) = Chronological Age (weeks) − Weeks Premature Weeks Premature = 40 − Gestational Age at Birth
Result: Chronological: 26 weeks; Adjusted: 18 weeks (~4.2 months)
A baby born on August 10, 2025 who was 8 weeks premature (born at 32 weeks gestation) is 26 weeks old chronologically by February 10, 2026. Subtracting 8 weeks gives an adjusted age of 18 weeks, or about 4.2 months — the age used for milestone comparisons.
A full-term pregnancy is 40 weeks. Babies born before 37 weeks are considered premature. Very preterm babies (under 32 weeks) and extremely preterm babies (under 28 weeks) may need adjusted age tracking for longer periods.
Adjusted age is most important for gross motor milestones (rolling, sitting, crawling, walking) and cognitive milestones (babbling, first words). Growth charts may also use adjusted age — ask your pediatrician which charts they prefer for your preemie.
Around age 2, most care providers switch to chronological age because development gaps have typically narrowed. If your child still shows delays at this point, early intervention evaluations can help determine if additional support is needed.
Adjusted age (corrected age) is your baby's chronological age minus the number of weeks they were born early. It reflects where your baby would be developmentally if born at full term (40 weeks).
Most pediatricians recommend using adjusted age for developmental milestone tracking until age 2. Some use it until age 3 for babies born very prematurely (before 28 weeks). Your doctor will advise when to stop adjusting.
No. Vaccinations are given based on chronological age (actual birth date), not adjusted age. Premature babies follow the same immunization schedule as full-term babies from their actual date of birth.
Late preterm babies (34-36 weeks) may benefit from adjusted age for the first few months but typically catch up quickly. A baby born at 36 weeks is only 4 weeks early, so the adjustment is small. Ask your pediatrician.
Most premature babies catch up to full-term peers by age 2-3. Babies born extremely early (before 28 weeks) may take longer. Early intervention services can help support development if delays persist.
Subtract your baby's gestational age at birth from 40 weeks. For example, a baby born at 34 weeks was 6 weeks premature (40 - 34 = 6). This number is used to calculate adjusted age.