Can you tell me exactly when is a period considered late?

When: If you have regular periods, it is late if it does not come at the anticipated time. Reasons for missed/late periods: low body wt, obesity, marked wt ^ or v, over-exercise, endurance athletics, breast-feeding, ^ stress, illness, eating disorders (bulimia or anorexia), anovulatory cycle (no egg released), travel, hormone irregularities, drug use, meds (i.e., birth control) & pregnancy.