According to medical studies, the average of menstrual cycle is 24 – 38 days long. If your period is late after that, you probably think that you are pregnant. If your pregnancy test shows negative result; it's logic to wonder "why my period is absent?"… Through this topic we will highlight the most significant possible causes of missed period.
1.    Low-caloric diet: following healthy well-balanced diet has many benefits for health, but if your intake of calories is extremely lower than your body needs, especially if accompanied with vigorous exercise, you may experience missed periods or what is known as secondary amenorrhea.
2.    Stress: it's noted that frequent exposure to massive stress could be responsible for missed periods.
3.    Hormonal contraception: using of oral or injectable contraceptives may cause amenorrhea as these contraceptive methods cause inhibition of ovulation, which in turn leads to missed periods.
4.    Polycystic ovary syndrome: it develops due to imbalance of hormones responsible for ovulation, so it's mainly manifested with amenorrhea and hirsutism.
5.    Thyroid dysfunction: hyperthyroidism or hypothyroidism may be manifested with irregular or missed period.
6.    Reaching perimenopause stage: perimenopause stage is a transitional stage between fertility period and menopause (lasts about 1 – 2 years). During this stage, irregular or absent periods are very common.