I am 40 years old, and my period is 13 days late. how likely is it that i am pregnant? or is there something else that could be causing this?

Menstrual cycles: It is common to skip or be delayed for a menstrual cycle as you get older and as you approach menopause. Still, if you are sexually active, you could be pregnant. I would check a pregnancy test to see if you are pregnant. If not, i would track your cycles to see if it happens often and see your doctor if you notice that it becomes more irregular.

Pregnancy likely?: Many different reasons exist, obviously pregnancy should be excluded first. Diet changes, sleep changes, stress, and exercise changes can also affect menstrual regularity. Although you are still young, menopause can affect women of a broad age range.