After waiting the stipulated time, if you haven’t received any response or feedback from the interviewer then it is polite to contact them and ask about the status of your interview. Mention that you are very keen on knowing the results. However, do not be pushy or aggressive in your tone. Thank them for their time once they inform you about the result. Emailing is always the best and most professional way to follow up. Unless you have been told by the interviewer that it is okay to contact them via phone.