The premature infant: How old is my baby?
Babies who are born prematurely often have two ages:
- Chronological age is the age of the baby from the day of birth—the number of days, weeks or years old the baby is.
- Adjusted age is the age of the baby based on his due date. Health care providers may use this age when they evaluate the baby's growth and development. So, if a baby is 6 months old, but was born two months early, his adjusted age is 4 months.
This is up to you.
- You can say, "He's 6 months old, but he was born two months early. That's why he looks like a 4-month-old."
- Or you can say, "He's 6 months old" and leave it at that.
Remember: When people ask about your baby, they usually are being kind, not nosy.
- Chronological age: 20 weeks
- The number of weeks your baby was premature: 6 weeks
- Subtract the number of weeks premature from the chronological age (this is your baby's adjusted age): 20 weeks minus 6 weeks equal 14 weeks.
- Divide your baby's adjusted age in weeks by 4 to determine your baby's adjusted age in months: 14 divided by 4 equals 3 ½ months.
See also: Share your story
Last reviewed August 2014
Frequently Asked Questions
How do I calculate adjusted age for preemies?
Chronological age is the age of a baby from the day of birth. Adjusted age is the age of the baby based on his due date. To calculate adjusted age, take your baby's chronological age (for example, 20 weeks) and subtract the number of weeks premature the baby was (6 weeks). This baby's adjusted age (20 - 6) is 14 weeks. Health care providers may use this age when they evaluate the baby's growth and development. Most premature babies catch up to their peers developmentally in 2 to 3 years. After that, differences in size or development are most likely due to individual differences, rather than to premature birth. Some very small babies take longer to catch up.
What does it mean if a baby is born “late preterm?”
Late preterm means that a baby is born after 34 weeks but before 37 weeks of pregnancy. It's important to try to have your baby as close to 39 weeks of pregnancy as possible. In the last few weeks of pregnancy, your baby's organs, like his brains, lungs and liver, are still growing. Waiting until you're at least 39 weeks also gives your baby time to gain more weight and makes him less likely to have vision and hearing problems after birth. Your baby will also be better able to suck and swallow and stay awake long enough to eat after he's born. Babies born early sometimes can't do these things.