Can a woman be late on her period and not pregnant?

Yes, it's possible. Many women have irregular cycles. Causes of late periods can be -- - Major weight loss or gain - Stress: Affects hypothalamus which is the major controller of our periods - Thyroid irregularities - Due to birth control methods too - Chronic disease leads to general stress, results in missing periods - Premature menopause - Polycystic ovarian syndrome: A condition which cause hormonal imbalance, leads to cyst around ovary, and thus, miss or late periods.