I guess id like to know your personal experience as well as what doctors say too...don't just tell me how long it takes a cis girl cause I know its not exactly the same unless you start that young yourself...also is there a chance that younger girls have a longer time of development?

I'm 3 years in and I started at 21. My doc says I should have full maturity. According to my endo I'm at tanner stage 4 (second mound appears). Apparently I'm well within the average range of time they take to mature but I think I won't reach stage 5 until I have grs.

To be honest I think it all comes down to genes.

FYI: I'm IS

I've had small breasts since I was 10.  Since being on ERT for twenty months, I really haven't had much growth.  I wear a 38B bra. Even my HRT doctor is a bit concerned. 

However, from what I've heard, those with AIS tend to be tall and slender, which i will be, when i lose weight.  And honesty, I'd just be happy with about where I am, i just wish my right boob would caught up :-).

There are a few studies that show breast development (not necessarily size) for most trans women is 2 years:

https://www.susans.org/forums/index.php/topic,186343.msg1659066.html#msg1659066

So by 2 years, maybe 3 tops, you should have all the structure there's going to be.  Of course they'll grow and shrink and change shape over your whole life based on your weight and age. 

If you're in your 20s you have a greater chance of reaching Tanner stage IV or V, and a greater chance for a larger initial cup size, but the actual time should be the same (under 3 years).

It's definitely about genes.

My mother's side is petite, my father's buxom.

My puppies are coming along nicely at 9 months ... oh, started at 35.

  Err, not young, took a few years, 34'ish B, about 2 cup sizes below Mum... but I knew I would not get to her size...
But it depends on Age, Genes, your internals etc... and It can still take a few years to reach maturity...

L Katy

It's also about hormones and surgery. People note changes after both surgery and changes in hormones (I have just changed mine and my breasts are tender and have definitely had a growth spurt again - after being on hormones for two years).

Together with genes, age, surgery, hormones and other factors, there are two many variables to give anything other than a vague guideline of 2 years and you are probably about there.

It took mine about 2 and half years to grow to there current size (a D cup). I started at 21.

I actually wear the same cup size as my mother, but a bigger band.. I am a 36 and she wears a 34.. so technically I am bigger than her.  The women in my family from father and mothers side were big breasted like DD or DDD, so I think those genes affected me too. My mother and I are the only ones with D cups.

I'm 36 and growing faster than some girls who started in their teens.

Age aint nothin' but a number baby, but being younger does seem to help. Fortunately I have really good genes on my mom's side.

I've also had lower T than most cis males throughout my life so that may have helped.

I come from a small busted family except back at my maternal grandmother, who was a D. My mother was a C, my sister is a C, and my daughter was an A until she had BA. We've chatted and she said her breast development was very like my own until her BA several years ago. She's very happy with that choice.

I am currently a reasonably full A and I've not seen much growth over the last year despite adding progesterone. There's been a filling in of what's there, increase in the areola size, some increase in nipple size but nothing dramatic compared to the first 18 months so I've opted for BA when I do GRS this summer.

I don't see why it wouldn't be more or less the same as cis girls since we're starting with the same physical "canvas" as a pre-pubescent girl (aside from rib cage/frame size, but that will affect how the breasts *look,* not how they develop).

That aside, I'm 5+ years in and seeing a bit of fat deposition and rounding out still happening. Started at 32, Tanner V for at least 2-3 years now.

Like Grace says, I suspect it comes down to genes. I developed fast and curvy, and recently had a chance to chat with my sister and found out she was similar, in that she went from totally flat to fairly busty within a couple of years...

It's a gene thing. I began estrogen at 13. Blockers did not exist at the time -- that I know of. I had eight sisters at the time (nine now).  Breasts on maternal side are D's+ and A's/B's on paternal side. Females are voluptuous and curvy on maternal and athletic slim build on paternal. I maxed out at around 16 years of age at almost a C cup and 34 beneath the breast. I surpassed some of my sisters who inherited the paternal gene.  We did compare our breasts growing up and still do at times. My cup size increases and decreases with weight loss or gain.  One thing I and my sisters have noticed is that my breasts are firmer and perkier with no 'gravity was here' droop. I give credit to my daily estrogen pill. Only the oldest and youngest inherited the curviness of the maternal side but that is okay because as I age it would have played against me.

In summary, it took my cis-sisters and I almost the same amount of time to develop except for the youngest and oldest who inherited the maternal gene. The doctor always said I was coming along nicely so I gather development was on point.  The trans-sisters who started out later in their latter teens seemed it took longer for some reason and I would think it was because of the testosterone in their systems.  Let me know what conclusion you arrive at.