How/When to tell the father?

My BF and I are in our last semester of grad school. It's an incredibly intense program and we're both under a lot of pressure to perform well. Our graduation is April 29. I'll be like 14 weeks I think by then.
We've been together for 6 years but I know he's NOT ready for this. We're 26 & 27. From a financial standpoint I'm not exactly ready either, but I know with my degree I'll be able to find a great job (just might be hard at first cuz I doubt I'll have worked there long enough for maternity leave by the time I give birth). But I know I'll figure that part out. My parents were much younger and much worse off than I am and I feel ready on every other front besides my career. I want this kid. I realized I'm more scared of him leaving me than I am having the baby, and that's not a good enough reason to abort in my book. He's not even ready to move in together "for a few more years" so I doubt he will want to stay.
I will be heartbroken if I have to do this alone, but I know that I can if it comes down to it.
My question is whether I should tell my BF now, or if I should wait until we graduate? 
I know if I tell him now with the stress of school he will NOT react well. It could potentially jeopardize his performance on top of that and I don't want to do that to him. I'm hoping that if I tell him after graduation when he can "breathe" that he might react better. 
The only problem is I'm leaving for a study abroad 4 days later. So there won't be much time to process things before I leave the country. Telling him when I get back isn't really a good idea cuz I'll be like 18-19 weeks at that point and it will just feel deceptive to come back from the trip with a big ol belly.
Please help. Also, any advice on the wording for when I actually tell him? 
I want to make it clear that I would love him to be a part of this but that I can do it alone if he's not up to it.