The answer is, it is a personal preference between two totally common and widely accepted options:
1) Apr 2017 - Sep 2017 (If you're going to abbreviate the months, don't forget the periods. For example, Apr. )
2) To be completed Sep 2017
That's it. Done and done.
Here is why (in case you're interested):
Most (if not all) companies realize the very definition of an internship includes a set time period. (Yes, there is a different type of internship where there isn't a defined end date, but that's the lesser known type. Most companies hear "internship" and will ask, "when does it end.") Most internships are a pre-determined time period (usually 3 or 6 months).
This question reminds me of folks who are in the middle taking classes that they mention on their resume but haven't finished the course yet. Same idea applies.
It also reminds me of resumes of people (like me) who do contract work. Although contract jobs are offered by staffing agencies/temp companies, the reason it's called a "contract" or a "short-term" position specifically, is because there is a start date and an end date. Not all temp jobs are short. People can work as temps for years at the same "assignment".
Job ads that read, "Contract position available for an Administrative Assistant, 6 months, for our client (they usually don't tell you the clients name until you call about the job) in any-town, any-state for $23/hr. If interested, please call XYZ Temp Company.
Many times a position will be listed and it's only until you email or call to apply that they tell you the details and that it is, in fact, a short-term assignment for XYZ company and the rate per hour you will receive.
Hope that helps!
