How do you tell your parents you are moving out?

I am an 17 year old who will be 18 in two months. I still have a year left of high school. My home life is unsatisfactory and I am aware that part of it is my fault. I have lost complete trust in my parents because of my grades and skipping class that was just a bad decision on my part. The problem is no matter how much I try to show my parents that I have learned from my mistake they never seem to care.

My mother has severe anxiety and so does my little brother who also has autism. My mother has a controlling overbearing personality that constantily butts with my personality, we never go one day without fighting. She has told me for a while that if I don’t like things the way they are that I can just move out when I turn 18, but what she says and what she means are two different things, I am almost positive that is she is going to have a fit when I tell her I don’t want to live at home anymore.

The reasons why I want to move out are that I have restrictions on how many hours I can work, I also have to quit my job after the summer is over because they don’t think I can handle my job and school work. I am constantily brought down and then brought up, I get yelled at and told that I am a disappointment and then later in the day told that I am not and that I am a great kid. I know my relationship with my parents will be better when I move out, I plan on keeping my job, moving in with two friends into an apartment and then finishing high school and going to college, with or without their help.

My question is, how can I tell my parents without them getting upset, I don’t want to tell them now, but I don’t want to wait until the night I leave either. I don’t want them to have a grudge against me or be angry at me, I want them to understand that this is my decision and that I just need support. Should I write them a letter, sit them down, tell only one parent or tell them both? I am very, very confused and any help on his matter will be greatly appreciated!