Do NOT answer this! Any employer who asks this is working outside of legal and ethical boundaries and you can expect more of the same from them should you choose to work there. This is no one's business and has NOTHING to do with your performance or work habits. This is not technically illegal, but think about it, it's right up there with "do you have children?" and "what does your husband do?" When I was asked this ages ago, I covered up my left hand (ring finger) and said plainly, "I don't have any obligations that would interfere with my ability to do my job." I got the job but should have listened to my gut-it turned out to be an awful place to work!