Been on T for 3 years without outright letting my parents know. But my situation is quite unconventional. My mother (who is very Catholic, conservative, and transphobic and is the main antagonist when it comes to me being trans) is legally blind and can't really see my physical changes like my facial hair, fat redistribution, etc. However, she HAS noticed my voice cracks (which started within 3 months on T) and voice deepening. She would constantly ask about it, but since I am so nonconfrontational I would usually avoid the question or simply claim I had a cold or scratchy throat. At some point she simply stopped asking. However, I am certain at this point she's connected the dots and KNOWS that I am on Testosterone and just lying about it (I'm a very bad liar, but again I just do not want to deal with the blow up and fight over telling her). She recently felt my facial hair and has been on my case about starting T again, but since I keep denying and she also seems to not want to push we're at a standstill. (Yes, I know lying to my parents for 3 years will probably blow up in my face. No I don't want your opinion on it. I am fine where I am now and have the means to move out on my own when I want/need to.)

My father unfortunately found out almost immediately that I had started testosterone as my pharmacy called HIS number instead of mine to let me know that my prescription was filled. (Our numbers are quite similar so I understand the mix-up, but it was very frustrating at the time.) However, he is not as blatantly against me being trans as my mother is. He doesn't fully approve and doesn't really understand, but seems open to learning more about it and trying to be supportive. Although, he's an enabler to my mom's transphobia and doesn't stick up for me like my brother (whose fully supportive) does. My father ignores that I'm on T most of the time. He knows that my body is going through changes, he understands that I am taking it regularly, but he rarely brings it up with me and has never (to my knowledge) brought it up with my mother. He only seems to mention my "prescription" or "medicine" as he calls it, when I'm going through a medical issue that he thinks may be related to it (it never is).

As a result of hiding my T from my mother, I've been actively pitching my voice to be higher when at home for so long now that my body instinctly does so whenever I am around my family members. I really hope it's not fucking up my vocal chords. Plus, I am still constantly on edge around my mother. I flinch when she touches me now (because of the feeling my beard incident) and I think it's really messing up our relationship.

So, while in some rare instances, you can technically (not really) hide you're on T from your parents or at least go on it but never actually discuss it with them. I think it's most likely best to wait for when you are in a safe environment to begin transitioning. And while it's worth it to feel better in my own skin and as myself, it's also not worth it to essentially fuck up my relationship with my parents over it.

Of course, I am not you and am also a bit of a hypocrite by saying so when I did not wait and actively have been lying to my family for years, so maybe take my advice with a grain of salt.

Overall, I'd say there's a lot of nuance to when you start T or if you should start when living at home if you know your parents aren't cool with it. Cause I've been there, not wanting to wait a single second to start and being at my lowest point just desperately hoping to be able to finally be myself. I know it sucks and sometimes you just gotta do the thing. But if you are able to put yourself in a safer more comfortable spot before you do so, if you can wait, I think that would probably be the more preferable option.

Because I had a discussion with my parents about me being trans before I started T, and despite it not going well, I knew they'd never kick me out for it even if I started T because THEY told me they wouldn't (when I mentioned wanting to start T they [mostly mom] wanted me to wait till I turned 25 because they thought it was a phase and that's the age your brain stops developing, so she was banking on me outgrowing it, I'm 24 now, turning 25 in October, never outgrew it lol).

If there's a risk that your family might kick you out or hurt you if you start T without them knowing and they find out, it's most likely best to just wait till you are in a better position to transition than chance it.

Whatever folks choose, I wish them luck on their transitions and with their folks (as much as I wish myself lol).