Hi,I have looked at several sites,but couldn't find what I was looking for.My question is:How can I calculate how long my cycle is?I always have a period every month,but they are not always regular.For example,35,29,30,33,33,27.So how do I get an exact number.It makes it hard to predict ovulation.There is a chance I'm pregnant now but I won't know for a few more days.