A period that is always late may indicate a longer than usual menstrual cycle, according to Everyday Health. While most women's menstrual cycle is 28 days, up to seven days plus or minus this is considered to be normal. If the cycle is longer than this, reasons for a late period can include emotional or physical stress, dieting, birth control pill use or a variety of underlying health problems.
Subtle hormonal imbalances are often to blame for late periods, according to Everyday Health. Any excessive stress on the body can cause fluctuations in estrogen levels that can cause irregularities in the menstrual cycle. Excessive exercising, illness, weight loss or gain, and chronic or short-term stress can all throw off the timing of the menstrual cycle.
Though rare, several medical conditions can also affect the timing of the menstrual cycle, according to Everyday Health. Thyroid disorders can cause thyroid hormone blood levels to go too high or low, causing late or missed periods. Other health conditions that can affect the menstrual cycle include diabetes, sexually transmitted disease, fibroids, eating disorders and endometriosis.
While one late period is not cause for concern, consistently late or missed periods are, according to Everyday Health. Women with continually irregular periods should visit a doctor to discuss symptoms and be evaluated for underlying conditions.