Pregnancy, stress, excessive exercise, dieting and hormonal changes often account for a period to be three days late, according to Summit Medical Group. A period is not considered late until it is five days late; however, normal fluctuations can happen in the menstrual cycle that can cause an otherwise regular menstrual cycle to be several days late.
If pregnancy is possible, a period that is three days late can be an indication of this, and a pregnancy test should be taken, according to Summit Medical Group. Physical and emotional stresses are the leading causes for a period being a few days late. Physical stress can include illness, rapid weight gain or loss, excessive exercise, a sexually transmitted disease, going on vacation or making other changes to a regular schedule. Emotional stress can include a break-up with a boyfriend, depression or changes at work. In rare cases, polycystic ovary syndrome can cause a period to be late; however, this is typically accompanied by increased body hair, acne and weight gain. Stopping birth control pills can also cause a period to be late or irregular for one or two menstrual cycles. To help in maintaining regular menstrual cycles, women must eat a healthy diet, get plenty of rest, exercise regularly and practice some type of stress relieving activity.