What will happen if I tell my therapist I self harm?

I'm glad that you're thinking of telling your therapist that you self-harm; it's so important for them to know. There's no clear cut answer though to how they will respond, as every therapist is a little bit different. The main priority with self-harm is to make sure that you are safe. They will probably ask you if you are having suicidal thoughts and they may ask you more about the self-harm. Things like what you do, how often and what sorts of things trigger it. Learning and talking more about your self-harm can help you manage it. If you're not comfortable talking more about it that's up to you too - this is between you and your therapist.

I'm not too sure about countries other than in my own and the USA, but there should be some level of confidentiality involved in the therapy profession. It's best to ask them to make sure "What things are kept confidential, and what do you need to tell others?" Sometimes, some therapists will tell your parents about it, but that shouldn't deter you from telling your therapist! It'll be discussed between you and them beforehand, whether or not and how they will tell. But they will most likely ask more about the self-harm, with some possible questions including: how long you've been doing it for, why you do it, when you do it and how you feel before, during, immediately after and a while after doing it, how you self-harm, what causes you to self-harm, if you're having thoughts of suicide etc. You might both come up with coping strategies or distractions as well, but it's all depending on your therapist. Good luck, and well done on thinking about telling them! It's a really brave thing to do.

They will assess how bad it is and that if they need to contact additional support for you. However if they feel that you are safe and wont harm yourself to a point that your life is in danger they will provide you advice and support to overcome this.

I have told my psychologist/therapist this in the past. I was scared to, believing he might tell me off or look as me as weak or attention seeing afterwards. But he went on to ask what caused me to do this and why, and asked if I were ok and what we could do to try and prevent it happening again. I believe a therapist definitely shouldn’t or will not judge you. They should make sure you are safe, and go about trying to find ways that will prevent self harm from happening (or at least being less likely from happening) in the future.

Well your therapist would give you advice I guess. Or try to help you to the best of their abilities