I'm not sure if this counts as advice, but parents can surprise you a lot of times. My mom could FREAK about the littlest things, (like oh my god you used the last towel you bitch devil-child), but when there was something big (like when I ran away for a weekend and came back filthy and just wanting to take a shower), she was very reasonable about it. I walked in the house and said something to the effect of "I'm sorry. It won't happen again. I want to shower." She just said ok. I don't think she even punished me, which is crazy because the cops had been called and everything.

I hope everything goes well for you! Chances are they will call your parents in and prompt you to tell them while they act as a mediator for the situation. It will be hard, but good on you for seeking the help you need. Good luck!

I will never forget the night I told my step-mom about my self-harming. I was 12 years old and we had gotten into some stupid fight that had prompted my child mind to say "Go cut yourself you worthless excuse for a human." Now, I had done this before, but something about this night and the pain I had been holding inside of me for so long finally spilled over and I asked my step-mom to come to my room. Mind you, we had just had a screaming match moments before so she was still quite livid with me. When she asked me what I wanted I just cried and cried and cried. She was about to walk out of the room I showed her my arms and legs and said "Please help me, I don't want to do this any more." Her whole demeanor changed and we cried together and worked out a plan to get me into a counselor's office ASAP. Much like the poster above said, parents will surprise you. I am very proud of you for wanting to get help and I want you to know that there is life past self-harm, Especially when you are young. I wish you all the best.

Speaking as a parent, we are people who make mistakes. We often react to a situation without realizing what is really going on. We are not infallible. It is how we react when it really really counts that separates good parents from bad. So I will echo what the above posters have said - parents will surprise you. Once they see you are in serious need of help, they will come to your aid.

Never give up seeking help!

I am glad you have a friend to reach out to that is helping you out. It's not an easy thing to do. That in of itself shows strength. Has self harm been an issue for you in the past that you parents knew about before? If not, it may be easier for them to talk with the counselor as a professional (just my opinion). When you do eventually talk to your parents, though, be honest with what you are struggling with. I know it can be hard, but it could be really helpful to have the support of the people who love you the most and live with you.
Know that you aren't alone in this. You are doing great in seeking help!

I am glad you have a friend to reach out to that is helping you out. It's not an easy thing to do. That in of itself shows strength. Has self harm been an issue for you in the past that you parents knew about before? If not, it may be easier for them to talk with the counselor as a professional (just my opinion). When you do eventually talk to your parents, though, be honest with what you are struggling with. I know it can be hard, but it could be really helpful to have the support of the people who love you the most and live with you.
Know that you aren't alone in this. You are doing great in seeking help!