Have you ever been at the doctors and asked, "When was the first day of your last period?" And all you can say is something generic like, "Hmmm, a few weeks ago."
Period trackers can be seriously useful tools for not only being able to answer that question correctly, but for helping you to learn more about your body: how your menstrual cycle is playing out, when you're at your most fertile and which hormones are dominant, when.
They also play a huge part now in the women's sport area - with the ability to identify when, during your cycle, you are able to hit peak performance - more about that here.
Are period trackers 100% correct?
They should be—that is, if you're a woman who has a regular ovulatory cycle and who habitually updates the app.
While each app is different, using their own algorithms, they basically depend on your accurate input of info so that they can best generate an estimated day of ovulation, a five-to-six day fertile window, and the date of your next period. The longer you're tracking your cycle, the more data the app's algorithm has to work with, and the more likely it is to be correct.
What's an example of them being wrong?
Your period tracking app can be wrong if you're a woman with an irregular or variable cycle. "For example, if your cycle ranges from 28 to 32 days in length, the ovulatory window shifts three to four days each month," says Dr. Kudesia, a reproductive endocrinologist and clinical assistant professor of obstetrics and gynecology at Houston Methodist. "Though the app shouldn’t miss the entire fertile window, it may be unable to pinpoint the exact day of ovulation." Similarly, if you have a cycle longer than 35 days, there is, in Dr. Kudesia's words, "a substantial likelihood" that you're not regularly ovulating, which the app may not flag as possibility.
Can they ever be used as a reliable method of contraception?
First off, know that no period tracker offers 100% - or even 99% - protection from pregnancy. Secondly, there is a difference between a certified medical contraceptive app and period trackers. While period trackers certainly can show you your fertile Windows and in effect you can avoid sex during those periods (though the 'fertile window' they give may not be fully accurate), they can't stop you from having unprotected sex.
Thankfully, there are a bunch of period tracking apps available for download that make tracking your period really easy. From the paid to the freebies, check out our picks above.