How To Calculate Baby’s Age


How To Calculate Baby’s Age. How to know how many weeks translate to the number of months old a baby is.

Home holding baby

Many new moms find calculating the age of your baby slightly confusing. Your friend’s baby is 16 weeks old, while your cousins is 4 months old, yet that isn’t the same age. This post is just to quickly clarify that for anyone who needs to know.

You can count your baby’s age by days, weeks, and months. At some point, you move on to years, though I am still not there with Brayden, who is currently almost three. There are not only 4 weeks in a month (except February), so every 4 weeks of your baby’s life does not equal one month. Here is a quick chart reference:

How to calculate baby's age
  • 4 Weeks = a couple of days shy of 1 month (it will depend on which month your child was born in)
  • 8 Weeks = almost a week shy of 2 months
  • 12 Weeks = one week shy of 3 months
  • 13 Weeks = 3 Months old
  • 16 Weeks = about a week and a half shy of 4 months old
  • 17.5 Weeks = 4 months old
  • 20 Weeks = about 2 weeks shy of 5 months old
  • 22 Weeks = 5 months old
  • 24 Weeks = 2-2.5 weeks shy of 6 months old
  • 26 Weeks = 6 months old

You can see from this list that 4 weeks does not equal one month. Both ages can indicate developmental milestones for you, so be sure you are comparing correct ages when looking at developmental milestones as well as Babywise milestones.

So at what ages do you give people when they ask? I think that depends on your audience. When Brayden was a baby, I kept track of his weeks until he was a year old, then I moved to months until he was two. Then I did just turned two, almost 2.5, 2.5, close to three, almost three.

Newborn baby sleeping wearing a crocheted bunny costume

With Kaitlyn, I have made things easier on myself. I kept track of weeks until she was about 4 months old, then I did months. I am already moving to years, though she is 13 months old.

If someone who doesn’t have young children asks how old my baby is, I do months. Weeks usually mean nothing to them. If it is a nurse or a doctor, I do weeks up to 4-6-ish months. If it is another mother who also has young children, I do weeks up to 3-4 months then do months.

How To Calculate Baby's Age. How to know how many weeks translate to the number of months old a baby is.

My reasoning behind this is to give the person the answer they are looking for. A childless person usually don’t know how to equate months with weeks, and before I had kids, I always wondered why my friend wouldn’t just tell me how many months her child was instead of weeks. A doctor or nurse knows what needs to be happening with your child down to the week, so that is why I do weeks much longer. A week really can make a difference in the accomplishments of your child. Another mother with young children has a point of reference with weeks, so that is why I do that with her for a while. That is what I do–but you do what you want :).

Reader Comments:

  • brisnicki said…
    This is a funny post that I can _so_ relate to :)My DD will be 7 months next week. I stopped counting weeks at around the 3 to 4 month mark as I kept losing count of the week. She was born right at the beginning of the month so it was much easier to look at current date and work out her age from that.I remember a friend once telling me her daughter was now 27 months old.. I paused to count how many years that was when she explained ‘2 years and 3 months’. Oh of course… I would have got there eventually, I am just slow at my 12 times tables :)Child ages are similar to pregnancy gestation. As mother I counted off the weeks one at a time, but while ’20 weeks’ meant alot to me (first ultrasound) it did not mean much to the lay person. They’d rather hear it in months so they know how far you’re along based on ‘9 months’ 🙂
    May 31, 2008 8:24 AM
    Plowmanators said…
    So true Brinsnicki 🙂
    June 1, 2008 8:27 PM

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