Rescheduling an interview should always be your last resort. Unless you have no other choice, make your best effort to make it to your interview. It's the first step in ensuring a good first impression. If you have a good reason and can't make alternative arrangements, you can ask to reschedule, but keep in mind that it may be a deal breaker for the employer and you might not get another shot.
Valid Reasons to Postpone an Interview
Health. If you are contagious or feverish, definitely cancel. Showing up when you are clearly sick as a dog is not going to make a good impression. If you suspect that you are coming down with a cold or have a lingering cough, either tough it out and show up or call and ask if the interviewer prefers that you reschedule. Do your best to treat your symptoms so that you look and feel your best. Apologize and don't shake hands.
Personal. When you have an unavoidable emergency, such as a death in the family or other unavoidable situation, let the interviewer know. Give enough detail to demonstrate that the issue is serious enough to warrant a cancellation, but don't go into your whole life story.
Travel. If you are coming some distance for the interview and have run into a travel glitch such as a cancelled flight, let the interviewer know as soon as possible and discuss alternate arrangements. If you have gotten lost or stuck in traffic badly enough to cause a serious delay, call to give the employer a choice of rescheduling or waiting until you get there.
Work. If you are currently employed, unavoidable commitments can come up. A client visit is moved, a project reassigned. There is no sense to chance losing your existing job for the possibility of a new job, so weigh your choices carefully. On the one hand, you will look to like a person who takes their current job seriously, on the other, you may seem ambivalent about moving to a new job.
If You Must Postpone...
- Contact the interviewer as far as possible in advance. As soon as you know there is a problem - call.
- Pick up the phone and call if possible. If you must email and don't get a response, follow up to make sure they have gotten the message.
- Reschedule right away. Let the interviewer know when you will be able to meet and agree upon a date and time.
- Follow up with a note or email thanking the interviewer for accommodating the change.
- Be really well prepared when you do interview. You've gotten a little extra time. Use it wisely.