I very recently accepted an offer to start a PhD in October.

I am currently working full time in a related field for a charity. I only need to give 4 weeks notice and plan to leave at the start of September so I can relocate for the phd.

However between now and August, when I'll be handing in my notice, I have my annual review (in June) I'm not sure it's fair to me or work to go through this pretending I'm still going to be there.

Should I tell my boss I'll be starting a PhD in October before my annual review or tell them just before I plan to hand in my notice?

I would like to stay on good terms and continue to volunteer by time with the charity after I start my PhD.