Period Tracker: Determine When Your Period is Due

Updated in October 2023

Women who have a regular menstrual cycle (ie. a cycle that lasts for the same number of days each month), are able to accurately predict when their next period is due.

If your period is regular, you can use our calculator below to determine when to expect your next period.


What is a period?

Your period, or menstruation, refers to the days in the menstrual cycle in which you begin bleeding vaginally, up until it disappears completely. On average, a period will last for 5 days, but this can vary from woman to woman. Your period marks the first day of the menstrual cycle, and it occurs 14 days after ovulation in women with regular cycles.

Why should you know when your next period will start?

Knowing when your next period will start is useful for women to prepare for that day - there may need to be some minor adjustments to your routine. It can also be useful for booking gynecological exams, like a pap test which should be completed on a day you don't have your period.

Knowing when to expect your next period can also help to prevent pregnancy, as your period days are the days you are least fertile (especially in women who have a regular cycle).

What if you don't know when your last period was?

Unfortunately, there is no way to calculate your next period without knowing the date of your last one. Therefore, we recommend that you track your next period, so that you can predict subsequent ones.

Will the calculator work for irregular cycles?

Women with irregular cycles gave greater difficulty predicting their next period. This happens because each cycle has varying durations, resulting in periods landing on different days.

This calculator was developed around cycles that are regular, and therefore it is unlikely that it will calculate the correct period dates for women with irregular cycles.