Trying to work out when your next period is due may not be complex mathematics but is hard to do without a calendar and pen. So here is something simple to help you.
This calculator lets you put in the date of your last period and instantly see when you are next due based on a 28-day cycle. Of course not every woman has an exact 28-day cycle. If yours is 30 days then simply add two more to the date shown. If your cycle is 26 days you will get it two days earlier than shown and so it goes.
If you have an irregular cycle then unfortunately there is no way of predicting when your next period will be.
Predicting periods is never an exact science and even if you are usually regular this is not a guarantee that the next one will be on time. However this tool will enable you to get a fairly good idea of when to expect your next period.