How long can a woman be in delayed menstruation?

Doctor would like to know how long the woman can be delayed menstruation. Because usually the minimum cycle is 28 to 30 days, and there are women who spend more time ... until how much time can pass ... because since July 21 that was my last menstruation has not yet come this month and by the accounts I have 40 days now ?
Expert answer:

Up to 15 days late (or 45 days without menstruation), we physicians consider it perfectly normal and usually have not done anything about it, from 15 days it is indicated that if the pregnancy test is performed if there is possibility of pregnancy or other tests to your doctor as you see fit.