I still live at home with my parents.
It took me a little over three months to actually bring myself to come out to my mother. Partially because I wasn't ready, but also because she was really stressed with her job and her injuries at the time, and I figured that if the conversation was anywhere near as difficult for her as would be for me, then I needed to catch her when she wasn't busy/tired/stressed/upset. I told her that I needed to talk, and asked that we go somewhere private where we could both sit down. She asked if this was about school, and I told her no, it was about me.
The thing to keep in mind here is that I have always be close with my mother. Ever since I was eleven, I have suffered from depression. She also suffers from depression, and as she was the one who searched for therapists for me when I was younger, dealt with me when I was at my wit's end, etc., I've always been able to confide in her about things that are bothering me. As such, I considered her relatively safe to talk to.
When I sat down in the den, I found myself extremely nervous, and I kept starting and stopping, fumbling my words. At that point, she told me she was listening, and that if it would help, to know that she would always love me no matter what. While I sincerely doubted she would disown me, it was nevertheless comforting to hear that. I then told her that I had reason to believe I was transgender, that I've felt this way since puberty yet didn't want to put the pieces together, and that last October I realized I was in denial. I told her about how I felt about myself and my environment. About how I've felt out of place, and for some reason always found it easier to identify with women. She asked if I had ever cross-dressed, and if I had ever spoken to anyone about this before. So on and so forth.
What seemed to take me by surprise was her apparent lack thereof. Turns out, ever since I was young, she had suspected in the back of her mind that I was gay. Something about my mannerism, the fact that I acted different from other boys, even at a young age, gaydar, etc.. She mentioned that she had told a friend of hers whose teenage son claimed he was gay that "he may not simply be acting out to spite her, and that she needed to accept the fact that her son may in fact be gay;" that she could not in good conscience give her friend that advice if she were not willing to accept it herself. She even said that she'd accept whatever partner I brought home. I then had to remind her that I'm still attracted to women, and that sex really isn't a major source of dysphoria for me. Social roles and my appearance are far bigger problems. I guess she expect one sort of coming out and got another. : P
Anyway, she admitted she was familiar with the nuances of transgender, but is willing to learn; and that if I need therapy, then we'll find me a therapist, and if it turns out I need to transition, then she will gladly accept me as a daughter. She did mention that she was worried, because "I have a hard life in front of me," and that unfortunately, some people may never accept me as a result. Nevertheless, she loves me and is supportive.
I also asked about how should I approach my father about this, as I'm not sure how to do so. I don't think he'd disown me either, but I am afraid the news might not go over well, as I know some parents go through a grieving stage following a coming out. She offered to talk to him for me about.
Sorry, you probably didn't need the whole narrative. -_-'
Anyway, you know your parents better than any of us do. What is your relationship with them like? Any reason to believe they will or won't act in a certain way? I will say give yourself some time until you are ready, and try to approach them when you think they will be most receptive. How might you approach them if you had a different sort of personal problem? I can't tell you about starting transition before coming out, as I'm yet to start. The fact is, I'm scared to do anything drastic before I've had a chance to talk to a therapist, just to make sure transition is really what I want. In fact, I'm terrified of the whole process. As such, I can't blame you for being a fraidy cat, as I'm just as bad. I'm scared of, well, everything. Seriously.
I hope this helps, and I hope everything goes well.