Introduction
When a baby is born early, their age needs a second look. The Adjusted Age Calculator shows you two ages at once: your child's chronological age (the time since birth) and their adjusted age (also called corrected age). Adjusted age takes away the weeks your baby was born early, so you can track growth and skills from their due date instead of their birth date.
Doctors, nurses, and therapists use corrected age to judge milestones like rolling over, sitting, talking, and walking. A baby born at 31 weeks is about 9 weeks early. At 6 months old, that baby may act more like a 4-month-old, and that is normal. Using the wrong age can make a healthy preemie look behind.
Enter your baby's date of birth and pick a date to measure from (today or any other day). Then add the gestational age at birth in weeks and days, or enter the estimated due date instead.
The results include the math, step by step. You also see weeks of prematurity, the due date, charts that compare both ages, and a table of dates when your child reaches key adjusted-age milestones like 18, 24, and 32 months. The calculator flags the 24-month cutoff too, the point where it stops correcting for prematurity and goes back to plain chronological age. The American Academy of Pediatrics advises using corrected age during the first 2 years.1
This calculator is a guide, not medical advice. Always talk with your child's doctor about growth and development.
How to use our Adjusted Age Calculator
Enter your baby's birth date, the date you want to check, and how early your baby was born. The calculator shows your baby's chronological age, adjusted (corrected) age, weeks of prematurity, a step-by-step solution, and milestone dates.
Baby's Date of Birth: Pick the day your baby was born. It cannot be a future date.
Calculate Adjusted Age As Of: Pick the date you want the age for. It starts on today's date, but you can change it to a past checkup or a future visit.
Gestational age input method: Choose one way to tell us how early your baby came. Pick "Enter Gestational Age" if you know the weeks and days at birth, or pick "Enter Estimated Due Date" if you only know the due date.
Gestational Age at Birth (Weeks): Choose the number of full weeks your baby had at birth, from 22 to 44 weeks.
Additional Days (0 to 6): Choose any extra days past those full weeks. For example, 31 weeks and 4 days.
Estimated Due Date (EDD): If you chose the due date method, pick the date your baby was due. The calculator works out the gestational age from the birth date and the due date.
Calculate Adjusted Age: Click this button to see the results, charts, and milestone table. Click Reset / Clear to start over.
What Is Adjusted Age?
Adjusted age (also called corrected age) is a baby's age counted from their due date instead of their birth date. It is used for babies born early (premature). Weeks early are counted back from 40 weeks, the due date. If a baby is born at 32 weeks, that baby came 8 weeks early.1 So at 6 months old, their adjusted age is about 4 months.
Why Adjusted Age Matters
Premature babies need extra time to catch up. They were not done developing when they were born, so their skills follow a schedule closer to their due date.13 If you compare a preemie to full-term babies the same number of days old, it can look like the baby is behind when they are really right on track.
Doctors and therapists use adjusted age to:
- Check growth on weight, length, and head size charts12
- Judge milestones like rolling, sitting, crawling, walking, and talking
- Plan sleep steps, and sometimes feeding steps
- Time developmental screenings and checks for delays13
Shots (vaccines) are one big exception. Those are given by chronological age, not adjusted age.2
How the Math Works
The math is simple subtraction:
- Find weeks early: 40 weeks − gestational age at birth
- Subtract those weeks from the baby's actual (chronological) age1
Example: A baby born at 31 weeks and 4 days was 8 weeks and 3 days early. At 12 months old, their adjusted age is about 10 months.
Gestational Age Groups
The preterm groups follow the World Health Organization: extremely preterm is less than 28 weeks, very preterm 28 to less than 32 weeks, and moderate to late preterm 32 to 37 weeks.3 Early term runs from 37 weeks 0 days to 38 weeks 6 days, and full term from 39 weeks 0 days to 40 weeks 6 days.4
| Group | Weeks at Birth |
|---|---|
| Extremely preterm | Under 28 weeks |
| Very preterm | 28 to 31 weeks |
| Moderate to late preterm | 32 to 36 weeks |
| Early term | 37 to 38 weeks |
| Full term | 39 to 40 weeks |
The earlier a baby is born, the bigger the gap between actual age and adjusted age.
When to Stop Correcting
Adjusted age is used during the first 2 years.1 This calculator stops correcting at 24 months of corrected age. Screening tests count the 2 years on actual age: the ASQ stops adjusting when a child turns 2.10 By 2 years of age, most children born early have caught up to the typical milestone range.6 A child who has not caught up may need extra support for a longer period.6 Rules differ on when to stop. An older UK growth chart rule corrected babies born at 32 to 36 weeks until a corrected age of 1 year, and babies born before 32 weeks until a corrected age of 2 years.12 The UK's digital growth charts now correct throughout childhood.12 Follow what your child's doctor says.
Good to Know
Babies born at 40 weeks or later get no correction. Their adjusted age and actual age are the same. Adjusted age is also a guide, not a grade. If you are worried about your child's growth or skills, talk to your pediatrician. Help for a delay is likely to work better when it starts earlier in life rather than later.