Can stress cause your menstrual cycle to start early?

Answer 1

If you mean start early as in--the first time you've ever had a period, not that I know of. If I'm not mistaken, early onset menstruation is hormone related. Could be genetics as well.

If you mean start early as in--your period came at eg: 22 days instead of the usual 28 days, then yes. Stress can also make your period come late (like 32 days or so) or not have it that month at all.