Can exercising cause a late period and if so how late?

Maybe: Heavy exercise can cause a late period. How long it can be delayed varies from a few days to months. I recommend decreasing the activity, make sure you have increase your body fat. If there is no period after a month you should see your pcp because it can be from other reasons such as thyroid, prolactin, etc.

Endurance athletes w: Very low body fat, women who are over-exercising (esp with weight loss) or acute, marked ^ in exercise can cause late periods of variable duration.