I am already fully passable and have lived female for 4 years.  I am very feminine and my psychiatrist was actually surprised that I have never taken any hormones, he actually didn't know I was transgender (most people don't know, including my employer, etc.).  However I want to start hormones and maybe develop some breast tissue because I have nothing at all.  Also I heard that the longer you wait the more masculine you will become over time, so I need to get on it asap (have been putting them off because I wanted cryopreservation).  My facial hair recently began to be courser and I have to make sure to shave or there is stubble which indicates I need to get started right now!  To be honest I am really worried about gaining weight and getting a belly, because I was a gymnast and have always been really skinny and muscular (have 6 pack lol) still, but have read about the muscle loss and fat gain.  I have a severe high sprain to my left ankle that will take 3/4 months to fully heal to regular capacity, so I can't tumble and do gymnastics like I normally do, although I've started walking for exercise.  I just don't like the thought of metabolic changes when i can't run several miles to counteract whatever changes do happen.  I have made the appointment to go to an endocrinologist and I'm gonna see them this week.  I am worried about weight gain, because I don't have a family history of curvy women or full-cupped women, whether they are bigger or thin, and we don't have hardly any breast tissue (A-cups on both sides).  I figured I would write this and ask what you all think.  Thanks

Masculinization of your body is the result of the androgens in your system, most of which come from the testes, and human growth hormone, which regulates how your bones form and when growth plates fuse (though it is very much more complicated that that).

You are close to being done with puberty.  Starting HRT is going to limit any more of the androgen effects (if you are taking an anti-androgen) and emphasize and help create female attributes.  You should expect some breast growth, hip and buttock growth, facial changes with regard to adipose tissue, etc.

Males typically deposit fat in the belly area.  Women do not.  HRT should not cause you to get a "gut."

You will get that little pad of girlie fat over the bWaist
the roundness that drive men to do stoopid things lol.
Also not that it most likely will not go around your
Waist...just a little girlie contouring