You have 3 posts asking this so I am just going to cut and paste it through all of them. The only real way to tell them is just out with it. Beating around the bush with suggestion is going to confuse them and give them room for doubt and make you look like you even question it. Now whether you do this in a letter, email, text message, or face to face is up to you. Obviously the methodologies change based on method. Text and face to face are more immediately interactive so I am going to focus on that. Usually the easiest way is to lead into the topic using something currently in the news or such. you can sometimes pose a what if I was? to them and then out and tell them. Or you can do as I did, and just simply tell my mom. Course I was much older than you are now when I did that. My mom just said she always knew I was different. So it may not be as big a shock as you think, but whatever the reaction don't take it as 100% right off. There will be some shock to it and they will need some time to process positive and negative. They are going to ask questions, Do not get upset, they are trying to learn. If you want to write a letter or email, don't really beat around the bush, explain to them your feelings, how long you felt this way, how they can help, so on. In any of the cases show you have put a lot of thought and time into it. That's my suggestion.

Great idea

My wife’s response when I said “So I’m transgender...” was “Yea I know.”

So chances are they already know. Either they will accept you or they will try believe it’s not true. But after it’s out there and they see that you’re still you, it will get easier. For them. After you say it you’ll feel so much better.