When should I say I'm leaving my PhD program I am currently in my first year of a humanities PhD program at one of the ivy-league colleges, and I've decided to leave the program at the end of the  current spring term. (Yes, I'm 100% certain - I simply can't stand my field, dread every minute of my classes/research, and no longer desire to work in academia anyway. I also have been admitted to a certificate program elsewhere starting in the summer, and I have already accepted enrollment there.)

I do feel bad about quitting and want to tell my advisor and the director of graduate studies in my department that I'll be leaving at the end of May, so that it is not too sudden or abrupt. I have good grades and have never mentioned any problems with them out of politeness - none of my issues are the fault of the program; I am just a bad match for this work - so I'm fairly certain they do not suspect how I feel at all. I'm not especially close with either of them, but we do generally have a good relationship, I think. They both seem courteous and genuinely interested in helping me succeed in the program.

However, I am worried that if I tell them now, they will cut off my funding right away. (Normally, I would receive a stipend at the end of each month through May.) I need that money through May to pay for my current lease, which doesn't end until the summer. Basically, I would be in huge financial trouble if my funding ended now. 

Is that even what would happen if I told them that I had decided to leave though? I am leaving without even a Master's degree, so I'm worried they won't see the point in letting me continue through to the end of the semester. I believe my funding cannot be terminated until my academic review at the end of May (and only then if I haven't received good marks), but I don't know if this guarantee would be voided by my decision to leave.

I would appreciate any advice for this situation. I believe the right thing to do is to be honest about my intention to leave, but practically, I also need to consider my immediate financial welfare.
This is an interesting question and it’s really more about ethics than academia. 

I’m absolutely sympathetic to your position. You started your degree in good faith and have had a change of heart. 

If I were in your position I would probably give them notice 1 month before you intend to leave. Is that the ethical thing to do? No. I think, ethically, you ought to tell them now, but as you say it may cause you financial trouble. 

One thing you might do to mitigate your sense of taking advantage of the program is to be a good community member for this last semester. Help other students out. Volunteer for things when there is an opportunity to do so (like organizing seminars or even at the university level, like peer counseling) That way you can feel like the university is getting something back. 

Another option is to be honest and then if you get cut off just get a job to pay your rent until your lease is up. Your PhD stipend can’t be so high that it would be impossible to find a job of equal pay.