I am 40 years old, and my period is 4 days late. how likely is it that i am pregnant? or is there something else that could be causing this?

Many causes: Pregnancy is only one of many things that can cause you to have a late period. First, its always a good idea to do a pregnancy test to find out if you are pregnant as this is an obvious possibility. If the pregnancy tests are negative and its a persistent problem month after month, you should see your doctor and find out why. Best wishes!