Interviewers might ask this question to see how eager you are. It is less about your motivation, and more about your expectations for advancement, and whether or not you are realistic about growth opportunities. The most straight forward response to this question might be to say that you expect to receive a promotion when your level of achievement, accomplishments and the attainment of corporate benchmarks warrants it. Or, if you know the company where you are interviewing operates on a system of merit and standardized protocols for advancement, you might indicate that you would hope to be promoted according to the general schedule of in-house career advancement. Not all promotions are based on merit or achievement; some are based on length of tenure before any promotion advancement can take place. Finding out how a particular company handles promotion usually requires some research and networking with current staff, or with someone who recently left that company. Talking to both current and former employees might give a rounded picture of the promotional opportunities at that company. But take them both with a grain a salt. It stands to reason that someone who recently received a promotion will have more positive things to say about that employer, than someone who left the company because they felt they didn’t get treated properly and were overlooked for advancement. The simplest and most honest answer to the question, however is, “I expect to receive a promotion when I earn it.”