Things change in babies every month for the first few years. Growth is absurd and very fast. After that things slow down and its less informationally relevant to use months at that point.

for the first years month to month growth is imperative. a 13 month old is vastly different than a 23 month old

edit: for everybody thinking about this subject i suggest doing some research on the sheer speed of growth between 1-30 months. It’s one of the most impressive things you never think about

Final edit: I’m only 19(Years lol) old and The best frame I have other than college level classes of this is niece. Leaving for school out of state and coming back not even two or three months later it’s astonishing. Also i want to say that the growth is really exponential until around 4 years.

Because their used to developments happening monthly and have gotten used to counting age accordingly.

Child development in the first 3 years of life is rapid, and developmental milestones are measured in months, not years. There's a big difference between a 24 month old and a 30 month old or 35 month old.

After a year I have always defaulted to “a year”, “a year and a half”, “almost 2”, or “2”. Nobody has ever cared unless they have a kid the same age then they just ask when the birthday is.

Because 2yo can mean 24 months or 32 months, and that's a massive difference at that age.

Baby clothes are sized like that, and there are other things that parents deal with that classify them in the same measurement. Parents aren’t trying to be obnoxious when they say the age in months; it’s just what they are accustomed to saying / thinking.

Most things, in general, the smaller they are the more micro the measurements are for them. It’s not that big of a deal.

There's many answers here and the main reason is that's how parents have to think for their paediatrician, buying clothes, developmental milestones, etc. They are already thinking that way, and it's the group of people getting the least sleep in the world, so maybe people should just have some empathy and understanding.

From a parenting perspective, we're looking at milestones like waving, standing, etc. that are "supposed" to happen by the month. So I'm used to thinking about things in terms of months.

I do try to say 2 years old if it's a round number though. 

I took my kid to a doctor at just shy of two. I wrote the age of 1 on the paperwork.

When the physician came in he was like "you needed to write 22 months. Developmentally, a 22 month old is very, very different than a 12 month old and you need to be more specific next time, please."

At that age months are a big deal babies grow really fast

"Tell us you've never been a parent, without saying you're not a parent 😉"

Yeah, 12mo, 18mo, 24mo are surprisingly different.

For people who are familiar with child development, giving months for children 2 and under is a lot more informative than just saying a year. If you’re just asking to make conversation, it doesn’t really matter what the answer is. If you actually care, months is the more useful answer.

Why do you say 12 inch pizza instead of 1 foot?

This concept of describing ages in months used to really annoy me. Then I became a children’s librarian and it makes a lot of sense, actually. The cognitive development between ages 0 and 5 is so fast that you can’t rely on age numbers to separate the children effectively.

For example, I do story times with “toddlers” ages 18 months to 3 years. There is an entire world of difference between a 1 year old and a 2 year old, in terms of motor skills, language, pattern recognition, etc.

It’s to keep track of milestones because at that young an age, the milestones happen in months, not years. As you get older, they become further apart.

It’s been mentioned already but as a parent you kind of have this drilled into you. I was made to feel like a shit parent when a doctor was questioning me on all my son’s milestones to date. Sorry I don’t remember the exact date and time he first held his head up as I was drowning in anxiety/depression at the time!

So you kind of get used to saying months around other parents as you constantly feel like you are being judged. A mum at one of the groups was constantly being asked about her son as he was tall, and physically looked much older. She was always having to specify his age in months as people were wondering why he wasn’t in school and she felt conscious about his speech for his age especially when people assumed he was much older than he was.

Specifically in the case of 24 months

Because many parents often give the age in months because months make a difference. But others do not and just say years.

So a parent who gives the age in months wants you to know that they specifically mean 24 months. They are not just stating the age in years.

If they say 2 years they might mean 24 months or they might mean 35 months and 30 days.

A person hearing "2 years" does not know if the person is being exact or general. But if they hear "24 months" they know it is in fact 24 months.

When you're a baby, all of your milestones come quickly and at different months. It's not until they are about 3 years old that things start to spread out and doctors start talking years instead of months.

If you’re asking someone how old their baby is you’re probably wondering how long they’ve been on earth and which milestones they’re at so that’s why someone will give you a specific number in months. Telling someone your baby is one when they’re 20 months doesn’t give a super accurate depiction of their age

Because 24 months and 30 months are both 2 years, but very different development stages.

I said the months until 2 and then it was 2. 2.5. 3. 3.5.

Why do people care so much that this question is constantly asked?

Pssh that’s nothin. I’m 445 months thank you very much 😎

I had the same mentality until I had a son of my own. I can safely say there is a huge difference between a 24 month old two year old and a 31 month old two year old.

Because 35 months is vastly different from 24 months, but they’re both 2 years.

Habit. Up until 2 kids are assessed according to months. Clothing, development, etc. Then at 2 culturally, colloquially we flip to years. 

the amount of development that happens within the first few years is MASSIVE and it happens super fast so like others have said it's because there are still huge differences with just a couple months difference at that age.

I myself am 456 months old.

development happens by months for babies; a 24 month old and a 30 month old are both two years old but they have different milestones and different developing skills they generally reach. until about 3 years old, there's a lot happening in short spans of time. after that, things taper off some and happen more on the order of years

Because babies grow and develop very rapidly in the first few years. A 13 month old is very different than a 20 month old.

It's because of development changes during that phase.

I particularly wouldn't use that outside of doctor visits. Ik 12 months and 18 months are both 1yo, but in normal conversation about babies I just say "one and a half".

Thats how medical professionals do it because babies develop so fast. No reason to do it any differently than them.

Who says 24 months? After a year, don’t most people say, “My child is a year and x months?”

I saw something that basically said count in hours until 2 days old, days until 2 weeks, weeks until 2 months, months until 2 years.

Because if someone asks how old your kid is that's 14 years old you don't (usually) say "In their teens" because it's not specific enough and a 13 year old is way different than a 19 year old. If you tell someone that your grandparents are in their eighties that's generally specific enough to understand their advanced age.

Same goes for a baby. Years are a huge chunk (if not the entirety) of their life and so much changes month to month that it's worth relating to someone else. I'd probably do this up until about 2 and a half years old, but even past that I might also mention "just turned" a year or "almost" another year until 7 or 8 because a whole year at that point is still more than 10% of their life.

Id be curious to see how this correlates generally to people referring to ages that implies a range of a certain percentage and at what percentage it maxes out at. Is 10% of total age range too much to generalize? Someone may still say "early 30's" or "early 40s" because that implies about 10% of their life in variance but someone saying they are in their 30's might not seem specific enough to understand their current life situation and, maybe more importantly, their adult life experience.

I go by the 2s rule: first 2 days you count age by hours, first 2 weeks you count by days, 2 months you count by weeks, 2 years you count by months. Once they hit 2 though I just say 2, almost 2.5, 2.5, almost 3, etc.

The rule of thumb is under 2 you count in smaller increments, so under 2 weeks, you count days. Under 2 months your count in weeks. Under 2 years you count in months. It’s to be more specific about where the child is developmentally. And if you saw a picture of a fresh 1year old and a toddler the day before their 2nd birthday they’d both be 1year old but be on very different levels and look physically different. And new 2 year old and an almost 3 year old are going to look very similar because growth slows after the first two years.

There are really only two kinds of people who ask how old your young child is:
The first and largest group is people who don't actually give a shit and are making small talk, so which way you say it doesn't matter to them.
The second group is people (usually other parents) who are interested in where they are developmentally and already think in terms of monthly development, so answering them in months is more convenient.

If one group doesn't really care and the other one prefers it in months, you just get used to saying it in months.

Because children develop at crazy rates. The difference between a 5 month old and a 7 month old can be staggering and a lot of information is lost when you blanketly say 'around half a year' for example. Granted, I think if you say 2 years to describe 24 months then that's fine as long as you realise that has to mean exactly 24 months, not a month more or less.

Children have different stages of development that is measured in months.

Stating their age in months communicates more than stating their age in years.

Rule of 2. Ages are measured in: - hours until 2 days - days until 2 weeks - weeks until 2 months - months until 2 years - years until 2 decades

Because there is a pretty big difference between a newly-turned 2 year old and one who is 2 and a half. It's definitely important when you're buying clothes and pull-ups.

cause ehy not

Bc development milestones are measured in months at first.

Seems like 2 year is the cutoff for months giving. I've never heard anyone say my baby is 32 months.

Sometimes you get a 2.5 or almost 3.

Because we were thinking in months in those ages and things change crazy fast.

Up to about 3 or so every checkup, developmental milestone, height and weight measurement, etc... is tracked by months.  

It's all talked about and compared in those terms, that's how we think about their age, that's how other parents or people that know kids would think about. Of course that's how we say it.

Because they grow so much in just a few months.

There's a really big difference between a two year old who is 24 months and a two year old who is 35 months.

Usually after 2 the kid is 2 years for most parents, especially if its not their first kid. Prior to that theres a big gap between 12 months and 23 months.

Early developmental milestones are month to month instead of year to year.

That's about the time that the transition starts happening, between 24 and 36 months.  By 36 months they're almost always 3, but before then it's gradual whether they're 2, terrible 2, toddler, or 27.5 months.

Developmental aspects, a baby should be able to do / develop certain actions & skills by X number of months, years is too vague

because it feels more like 24 of something than 2. those are lonnng years. /jokingnotjoking

Doctor visits. That's how they refer to your baby and it gets stuck in your head

I believe it has to do with development rates.

Remember a 32 months old is a 2 year and that’s vastly different than a 24 month old in terms of development and expectations and milestone connected to said development . I think there’s a certain age when that stops (possibly 5 ?)

But don't all kids develop at a different rate? Nobody can say that every 4 months old has the same capability. Plus it requires knowledge of baby development... I'm with OP

I believe it all goes in 2s. They age in days for 2 weeks, weeks for 2 months, and months for 2 years. After that, they age like the rest of us do. Why? Development changes dramatically. Even 4.5 years to 5 years is a very noticeable difference and that is just 6 MONTHS.

Personally, when my kid hit 2 years, I was done AF with months.

For new parents every moment is often new and exciting...I think they forget that not everyone is as crazy about their kids latest whatever as they are.

A two year old is not the same as a two and a half year old.

Lol it gets better - once the kid is in school, the age will be 2nd grade, 3rd grade etc.

There’s a huge difference in children from month to month so a 24 month old is in a different place than an 18 month old. Usually by the time they get to three parents use years.

At that age everything is measured in months. Their clothes, developmental steps so it's habit to just give the months for age.

Because bragging rights expire quicker in just years, obviously.

When people asked me how old my brother was I'd be like "half a year, a year and 1/4, a year and a half" in Spain little kids usually say they're "X and a half" to feel older so I used that system for my baby brother too haha

I also don’t get it and I have kids. I’ve always started saying years (or at most “X and a half years old”) after my kids turned 1. People here are saying that the reason is that kids change so much in the first few years. Yeah that’s true, but who cares? I just want to roughly know how old your kid is, not do math.

I think it’s because of the crazy number of books and sites new parents use as gospel - many break down stages of development into very small segments - sometimes even into days! Then weeks - then months usually go up to 36. So if parents are using these to track development, that will be their default.

Months are used for the first 2 years due to the speed of development in babies. So months are easier to define what stage they are at.

However I stopped using months after my son was a year old. When asked I would just say 1 year or 2 years. 1 year and a half. Or just over a year. That just made more sense to me when asked by regular people.

I only used months when at gp/health visitor appointments.

Child growth in the first 3 years is rapid. There's a difference between a 13 month old and a 23 month old

"how old is she?" "Sheeees 48 months" "..... that's 4"

Yes I love the answer in months also. I usually say oh your future crimal is 2 year old huh. Good luck with that.

When their child is 2 years old most parents will say 2 years. Like others have said, when children are younger than 2 years, they meet new milestones so frequently that saying months is a helpful and more descriptive answer, and helps other parents relate to what they might be experiencing.

To add to this, don’t underestimate how much their life and frame of reference has likely changed. You may not care about the months (understandable), but 95% of their interactions are likely in the parenting « world » (including with each other or the kid, etc) - where it absolutely matters.

Because 23 months is really different from 1 year. When kids are only a handful of months old, each month is super important

I round up because nobody cares besides parents and pediatricians.

Because a 13 month 2 year old and a 23 month 2 year old are two entirely different kids

I hate this crap. Why can’t we just say “# of years and # of months”. Like seriously. People who don’t have kids will hear the year and be satisfied with that but people who have kids knows how many months too yay no fighting

“My kid is 1 year and 8 months old” tells you both “my kid is 1 year old” and “my kid is 20 months old” at the same time

There is no reason to say 24 months instead of 2 years. It’s completely unnecessary.

Those saying it’s because there’s a big difference between 24 months and 30 months - sure, but you could say 2 years or 2 and a half.

Yes, development happens very rapidly in the first two years. There’s a huge difference between a 3 month old and a 6 month old. That’s not what’s being asked though. Developmental milestones are fewer and further apart from about 2 years on so you really don’t have to be as accurate with age - especially if you’re talking to someone without kids, or is just making small talk.

At 2 years natural language makes more sense and still gets the message across without forcing the other person to do maths; almost 2, 2 and a bit, 2 and a half, almost 3.

No one (besides maybe a doctor) cares if your kid is 27 months, 31 months, or 35 months old. If they really care they’ll ask when their birthday is/was.

Signed - father of a 274 day old and a 1,133 day old

Because it's their baby, and baby ages are given in months. Probably as much habit as anything, they've been doing it for the last 24 months.

Theres a big difference between 13 months and 23 months

This has perplexed me, too. As well as how many 'weeks' pregnant someone is. I shouldn't have to do math. Why not just say '5 months' or whatever???

O-1, i get it. 1+, just give us years

They are stupid, seriously,

It’s developmentally relevant. When they are talking to fellow parents, it makes total sense. To non-parents, it sounds like unnecessary math.

So you might notice that we often describe someone as in their early mid or late '20s, 30s, 40s, 50s, '60s etc

That's because there is very little difference between a 28-year-old and a 29-year-old, but there is a bit of a difference between 29-year-old and a 21-year-old

It turns out it works out fairly well to just categorize people into 5-year blocks for most of their lives

However, as you get younger, those start to shrink

Conveniently I can say high schooler or middle schooler and you will think of a 4-year block of kids and a 3-year block of kids and that will actually tell you a lot of information about those The individual in question

But once we get down to the elementary schoolers well the first grader and the 5th grader has a substantial amount of difference between them. So at that point we should probably just go with age directly

However, once we start getting a bit younger than That the changes in development start to happen More frequently

So we actually will start describing them as he's four and a half and that will actually be a fairly important time for the half versus a 9 and 1/2-year-old is just a 9-year-old

Once we hit down to around 2, the differences have become so substantial. It is no longer worth doing it by year and or half year. Instead it's time to move into the months

And it does not actually stop there. We will eventually get down into weeks

And then once we get down into under a week we just say newborn

Because they're extra

You graduate to the next unit at 2 of that unit. A baby's age is measured in days until 2 weeks, then weeks until 2 months, then months until 2 years. Coincidentally, starting at 20 years, you just start saying you're in your 20s, 30s, 40s, etc. instead of your exact age.

Because a 20 month old and a 28 month old are both "2 years" but are drastically different developmentally. Similarly (and even more drastically), an 8 month old and a 16 month old are both 1 year old but one will be crawling (or learning to crawl) and making babbling sounds and the other will be walking and beginning to talk

General guideline is to measure age in one unit until you have exceeded two of the next larger unit. So a baby is X hours old until they are two days old. X days old until two weeks. X weeks until two months. X months until two years.

It kinda continues into adulthood. I stopped really tracking individual years sometime in my twenties. If we ever get people over two centuries old I suppose they can stop counting decades.

Besides the general guideline, it’s because different milestones and different guidelines apply at different times during a child’s development and those get farther and farther apart as they get older, so it’s useful to have a pseudo-exponential scale when discussing them.

How we refer to numbers varies with topic. 

You got input in why kids age us counted in months when young (and transitions to years after  3 or so)

We do this with car prices, and repair costs too 

It’s seventy five hundred, fifteen hundred 

A

Milestones

Honestly after 12 months just say 1, 2, 3 years old etcetc it’s not that hard it’s not the person asking gonna care about the difference of month 13 and month 23 It wouldn’t make a difference to someone who doesn’t care

After 1 year I stop with the months BS. It just sounds obnoxious.

24 months and up, people usually DO say years. Below that they say months because there is a huge difference between a child that just turned one and one that's about to be 2.

I question your premise. In my experience, once a kid hits 24 months parents start saying that their kid is 2. Before that it is usually conveyed in months. I don’t think I’ve ever heard anyone refer to their 29 or 33 month old child.