The last thing that any job aspirant would want is to come in late for the job interview. Would you want to already have negative marks even before you open your mouth to speak? Most likely not, right?
Of course, the best way to avoid this negative mark is to not be late at all. Being prompt for the interview might not give you the plus points, but it certainly puts you ahead of those who were late. Be careful not to become too early, by the way, because some HR professionals are actually annoyed by that behavior! Just come on time, probably early by five to ten minutes would already do.
But bad things do happen and, sometimes, we just cannot do anything to prevent the situation from happening. So what are you supposed to do?
Most sources say that the first thing that you have to do is to call your interviewer ahead of time. Apologize and give them a valid excuse why you would be late in the first place. Also ask if you can still continue with the interview right there and then or reschedule instead. Always remember to be courteous. If your excuse is valid and your interviewer is considerate, he/she might not take it against you.
Now, when you are already in your interview, you are faced with the task of proving your interviewer that being late is not the norm for you. You can still impress even when late. Just always, always be courteous when addressing him/her.
Finally, it would be in your best interest to not set your expectations high for this job. Some interviewers might not forgive anyone for being thirty minutes late (or longer) into the scheduled time. Rather than expecting to take the job, just be thankful that were allowed to go on with the interview and try to impress. If you still get it, then consider yourself lucky. You are one of the few people who have succeeded in arriving for the interview late yet still got the job. If you fail to get it, then it should be OK. Life must go on. Learn from your mistakes and do not do it again during your next interview.