During intercourse, a man, on an average, lasts from three to six minutes before ejaculating. This is calculated from the beginning of intercourse and is considered the normal range. However, premature ejaculation, which affects an estimated one-third of men, results in ejaculation within a minute or less of intercourse. There are many possible causes of premature ejaculation and sometimes it simply has a genetic component. Neurological conditions such as epilepsy, multiple sclerosis, and Parkinson's disease can also result in premature ejaculation. Don't worry - if you partner doesn't feel you ejaculate too soon, and neither do you - then there's no reason to be concerned or seek treatment.