My UK Tier 4 Visa will be ended in May 2016, and i can enter to UK Visa free not more than 180 days.
The question is: How long can I stay in UK? Must I have to leave in May OR June (180days from 1st Jan) OR November (June +180 days).
A T4 visa has traditionally added some extra time beyond the end of the student's course of study so that the student could spend some leisure time touring and gadding about before they left. This is accounted for in the expiry date of the visa, and there are no implicit extensions.
You need to be out of the UK by the expiry of your T4. They do not automatically add extra time after a T4 expires simply because the person is a non visa national (e.g., American, Canadian, etc). If you assume something like that you risk getting caught as an overstayer when you finally do exit. If you try telling them that you thought you automatically got extra time (or any other rationale along those lines), they will roll their eyes and serve you with a removal notice.
Part of the licensing process for a school to be able to sponsor T4's is that they have an administrative officer to explain things like this to their students. You would have received a letter when you first started identifying that person. You can print out this answer and show it to them to clarify your question along with any other questions you have.
Overall, they are getting very hair-triggered about stuff like that. They are making new rules that will be retrospective to October 2015...
Mrs May believes the current rules are being abused, with many students staying in the country illegally after their studies, BBC political correspondent Carole Walker said.
The good news: You can always clear UK exit controls to Calais, turn around, and get admitted as a visitor. If you have a successful landing interview, they will stamp your passport with a new expiry date. Sometimes it works, and sometimes it doesn't.