Have you come out yet? If not...
I came out to my mum over facebook while she was away on a trip. I was too nervous to talk to her about it to her face, I'm sure if I had come out to her face, there would have been yelling. The reason I came out to her was because I wanted to secure a ride to Toronto so I can meet the people that are needed to okay my transition(still haven't heard from them). While there is a medical transport system here, they don't go out as far a Toronto.
That's just my experience on it though, it would really have to depend on how your parents view such things. Do you know for a fact that you would be in a safe situation if you were to tell your parents? Would you have friends or more open relatives that live close by that would take you in if things were to go sour? Try to test the waters a bit, see what their opinions are of LGBT related things are, it might be difficult to drag into a conversation with them but maybe make a story up about a friend that wants to come out to their parents and you want to give them(the fictional friend) a way to talk with their parents about coming out. If your situation might not be as good as you were hoping it would be, try to keep your important documents in one place where you can easily get them should you be kicked out(also, have a bag of clothes ready in your room or by the door though I hope your situation isn't that bad).
If you're in a situation that might not be best to come out, consider coming out when you're older or when you're more financially independent. I might be making mountains out of mole-hills but I do want you to be prepared for anything. Coming out as trans is a different experience for everyone, what I still go through might be something that you never go through. I do hope that you have an easy time with coming out, sometimes you need to kick yourself in the pants to just get this type of thing out of the way so you can focus more on other things. You'll know when it's time to come out to them, I know you might want to get things moving(especially if you want to start dressing more feminine or start HRT asap) these things can take time and your parents may need some time to mull things over once you've come out to them. All I can really say beyond that is good luck with your parents. We're here, should you need us.