What are the PhD and Advanced Degree application deadlines for summer internships?
MBB allows PhDs to apply for the same summer internship that MBAs apply for, but it is far more rare for a PhD candidate to land this internship (priority goes to MBAs).
MBB also has week-long or weekend long internships introducing PhDs to consulting (app deadlines in Spring, event in Summer). Some of the other firms offer PhD summer internships as well (especially life sciences) but the priority typically goes to MBAs.
For 2020-21 deadlines, see this page.