Pregnancy is a commonly known reason for a late period, but it isn’t the only reason why a woman’s period might be 10 days late, according to WebMD. Other reasons for a late period include stress, severe changes in weight, medication changes, schedule changes or travel, hormone disorders, eating disorders, illegal drug use, illness, breastfeeding, peri-menopause, menopause, miscalculation and—rarely—certain types of diseases.
Pregnancy is a common cause of a late or missed period. Some at-home pregnancy tests can determine pregnancy within as few as five days of a missed period by testing for the hCG hormone, or “pregnancy hormone” in the urine, according to About.
HowStuffWorks suggests that women aged 40-50 years who experience a late period might be entering peri-menopause or menopause. Peri-menopause is when a woman transitions into menopause, which signals that her reproductive years are ending. Periods may become less frequent during peri-menopause and eventually stop completely during menopause. This can happen naturally or due to hysterectomy or chemotherapy.
Some women simply don’t keep track of their periods very well, according to About. Although the average menstrual cycle is said to be 28 days long, this is not true for every woman. It is possible for a woman to think her period is late when in fact she miscalculated or is just not aware of the average length of her individual menstrual cycle.