My menstrual is late for 40 days but show negative on pragnency test. why is it so?

"Tardy periods": At age 35, mother nature is starting to ovulate infrequently causing estrogen only menstrual cycles and thus longer period intervals. Stress and illness can also cause "aunt flow" to by later than usual.

Possible reasons: 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. #1 reason is pregnancy.