There are several situations that could give you good reason to cancel or reschedule a job interview. Regardless of your reasons for canceling the interview, do not cancel by leaving a voice mail message. Instead talk to a real person, whether it is the interviewer or her secretary or receptionist, to ensure that the interviewer does not expect you to show up.
A few categories of family emergencies make acceptable reasons to cancel a job interview. For example, a close family member might have just passed away and you need to attend the funeral. If a close family member, such as a child or spouse, is in the hospital with an emergency condition, this is also an OK reason to cancel.
If you are sick and at risk for passing the illness along to others, do the interviewer a courtesy and cancel your interview. Getting somebody sick does not earn you any points as far as a job is concerned. When you call to cancel, just say that you have come down with a contagious illness and will need to reschedule your interview for a later date.
Insurmountable Travel Delays
If you are traveling for an interview, you might find yourself unable to make it to the interview on time. A flight delay or cancellation could cause you to miss an out-of-state interview. Inclement winter weather that makes driving unsafe would also be an OK reason for rescheduling an interview as well. If at all possible, plan your travel for an interview so you will arrive early, which gives you room to absorb minor travel delays.
Don't Want Job
If you have absolutely no intention of taking the job if the company offers it to you, it is OK to cancel the interview. Not only do you save yourself the time and effort of interviewing, but you also do the interviewer the courtesy of not wasting his time. The most common situation that would lead to not wanting a job is if you have already accepted an offer for a better job.