What can cause a late period to occur?

Late ovulation: Late ovulation, hands down, is the most frequent reason for a late period (period starts late.) for a missed period (doesn't come at all, ) pregnancy is top of the list.

Late: Reasons for missed/late periods: low body weight, obesity, marked weight ^ 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) or medical problems (i.e. PCOS). #1 reason is pregnancy.