How do I take the plunge and just come out to my parents?

I feel like this is logically the right time to come out to them, and that not doing so will just build up the chronic angst in me, but there is no acute reason to deliver the shock to them. How have others dealt with taking the plunge?Background: I'm a gay male in my twenties, living in the UK, recently got my degree and have moved back home with my parents to start my career. I'm out to friends and some family (only some of those of the same generation). My parents are second generation immigrants and religious but not very strict. I can't be sure how coming out will go down with them but I think they would accept me after the initial shock - but I do think it will be a shock - they are clueless. I'm in a long term relationship with a guy who would love to be more involved with my family (which is a quality I love him for), and we would like to get a place together in the next year or two. So things are pretty good. But I don't see myself progressing without telling them soon, and I struggle to think about the future because of this big unknown. I don't cope well with change and neither do they. I'm worried about making them upset for months so there's always a reason to not tell them until after x event, y birthday, z christmas, etc. I've drafted multiple letters in case I can't articulate what I want to say in speech. But I have no idea how I will actually take the plunge.