How do I tell my parents that I self-harm?

This is a difficult question; as it really depends on the parents, but I can speak on personal experience. I told my parents through a letter, I made sure the letter was clear in how I was feeling and what they could do to help. I think that many parents get stressed when they feel helpless to support their child and so to avoid this I made sure to give them something they could do, for example arranging an appointment with a doctor. I also made sure not to blame anyone in my letter; your aim is to get better and passing blame creates confrontation. If you do feel as though something they do could be better, try to phrase it as something you should work on together, instead of directly saying 'you should..'. I also gave my parents time after reading the letter, so I avoided the primary emotional reaction and let them process the information privately. If you feel as though you cannot tell your parents though, speak to an adult you trust (ie a teacher or a doctor or another family member) about how you're feeling.

You can tell them you need to talk to them about something and then when an appropriate time comes, you can show them your scars or just tell them.