There are apps to track everything these days, from steps to calories to even how much water you’re drinking. Of course, a big one for a lot of women is period tracker apps, which can help record different aspects of your menstrual cycle. You can find out when your period arrives, how long it’ll last, and when’s the best time to become pregnant, at the touch of your phone screen.

But that’s not all these apps are good for. Your period is one of the most important vital signs for female health, says Apurva Shah, MD, an ob-gyn at Women’s Wellness Associates at Saint Vincent Hospital and the medical advisor at Mira. By keeping tabs on it, Dr. Shah points out that period tracker apps can raise a red flag to any potential underlying health problems.

The clue is usually any changes to your cycle or abnormalities—like irregular or heavy bleeding and severe pain, says Rashmi Kudesia, MD, a reproductive endocrinologist and clinical assistant professor of obstetrics and gynecology at Houston Methodist. “If something suddenly changes with your cycle or your period is late, you may not realize it right away if you’re not keeping track,” she says.

So, how do period tracker apps work? You just have to plug in some basic info like your basal body temperature (BBT), cervical fluid, heart rate, past periods, and sleep patterns, to name a few. (Your basal body temperature is the temperature of your body when it’s fully at rest. Ovulation can raise your body temperature ever so slightly.) The app then makes predictions about your next period and ovulation.

“In an ideal situation, menstrual cycles function like clockwork and this helps guide the user on their understanding of their fertile period,” Dr. Shah says. “This can then be used to either avoid or try to conceive. However, several apps go beyond this to predict various medical problems like PCOS and abnormal uterine bleeding.”

How accurate are period tracker apps?

It really depends on three factors—the accuracy of the data you enter, the relevance of the info you’re tracking, and the technology itself. “The more compliant the user is with input, the more accurate the predictions. The more objective the variable, the better the results,” Dr. Shah explains. For example, numerical values for hormones or BBT can contribute to a more exact read than a subjective assessment of cervical mucus. Also, a more up-to-date and robust algorithm is more reliable.

How long you’ve been tracking your cycle matters too. If you’ve been doing it for a long time, you’re giving the app more to work with and it is more likely to be correct with its predictions.

Yes, period tracker apps can sometimes be wrong, especially if you have an irregular cycle, Dr. Kudesia says. “For example, if your cycle ranges from 28 to 32 days in length, the ovulatory window shifts three to four days each month. Though the app should not miss the entire fertile window, it may be unable to pinpoint the exact day of ovulation,” she explains. Similarly, if you have a cycle that’s longer than 35 days, there is a strong likelihood that you’re not regularly ovulating, which the app may not flag as a possibility.

If you are interested in using a period tracker app, here are the 11 best period tracker apps, according to ob-gyns.

1. Clue

   Clue markets its app as being able to teach you about your body (because be honest, you weren’t paying attention back in sex ed class).

   With tracking options related to literally everything that goes on in your body during your cycle, like your period-induced breakouts or your PMS headaches, this one is pretty legit. It’s also Dr. Kudesia’s favorite app, and the one she actually uses herself.

   “I like its clean, modern interface, the impeccable science behind it, their transparent citation of supporting data, and the multitude of options you have for what you can track,” she explains.

   The Clue app is free, but if you are interested in learning even more about how your body works, you can sign up for Clue Plus. It offers enhanced period predictions and further analysis about your cycle.

    

2. Flo

   If you don’t use the Flo app already, you probably know someone else who does—it’s just that popular.

   Literally millions of users log in daily to record ovulation and period symptoms, turning their data into super useful graphs that show exactly what your body is doing and when. (These also come in handy at your doctor appointments, whether you think something’s up with your reproductive cycle or not.)

   Bonus: Flo also turns into a pregnancy tracker if and when you ever need it to, so it’s pretty all-in-one.

   Flo has both free and paid versions. The basic features are available for free while Flo Premium is optional. With a monthly fee, you will also receive a daily well-being plan, expert content, premium customer support, unlimited access to Flo Health Assistant, and video courses.

3. Ovia Fertility.

   If you’re really hoping to not get your period (a.k.a., you’re looking to get pregnant), the Ovia app might be your best bet.It’s technically a fertility tracker, so it really excels in helping you chart your basal body temperature, cervical position, and cervical mucus. But, unlike a lot of other fertility trackers, it has the ability to chart your period, too, and gives you predictions about your menstruation or fertility based on the data you input.

   Covered by some health plans and employers, the premium Ovia app provides personalized health support. Not eligible? Don’t worry, you can still access the free version, with the same great trackers and content.

4. Eve by Glow

   The original Glow app is one of the better rated fertility tracking apps out there, but the Eve version of the app focuses primarily on period tracking, in addition to letting you keep tabs on your sex life and gym habits. Dr. Kudesia compliments its clean and attractive interface, which features colorful, eye-catching graphics and icons.

   Eve by Glow is free to download and use. Should you choose to go premium, you can get premium content, comparative insights, a custom profile, premium support, and private messaging options.

5. MagicGirl

   If you’re new to getting your monthly flow (or know someone who is), the thought of tracking your period in an app might be kinda intimidating.

   Luckily, the MagicGirl Period Tracker was designed with teens in mind, so it makes learning the digital ins and outs of your cycle pretty easy. The app also helps you learn about hygiene product options, chat with other girls and get period advice, and remember to take your birth control pill (something we could all use help with).

   The bright interface will be instantly attractive to most teens, but it’s a fully functioning period tracker, so there’s no minimum or maximum age required for use. Another perk? It’s free.

6. Period Tracker Period Calendar

   Period Tracker’s Period Calendar is the top period tracking app on Google and consistently gets good reviews. A lot of that may come down to ease of use: It’s simple to navigate, straightforward in how you track and rate symptoms, and literally anyone—regular or irregular, newly menstruating or premenopausal—can use it. If you’re looking for an app that’s not fussy and gives you more than enough room to log all kinds of data, this might be it.

   Although this app is free, if you want the additional features, you’ll need to buy a monthly subscription.

7. MyFlo

   For women with irregular menstruation, women starting menopause, or women wondering why they’re experiencing other random cycle symptoms (think excessive bloating, migraines, constipation, or low energy), the MyFlo app promises to do way more than simply track your periods: It takes the symptoms you record and turns them into useful information about your overall health.

   My Flo can clue you into possible hormone imbalances and suggests lifestyle changes (like the best foods to eat or activities to engage in) that could make you feel better during different phases of your cycle. The app works great for women with textbook menstruation, too. Plus, you can unlock all features with just $1.99.

8. Cycles

   Cycles is ultra-customizable but also just looks good. With simple graphics and soothing colors, this is the period tracking app you want to download if you don’t want anyone to know you’ve downloaded a period tracking app (so you can semi-discreetly update it in public when you need to).

   It also stands out from the crowd for the fact that it gets your partner in on the tracking action: You can invite him to sync up with the app on his device so he knows what’s up with your monthly mood swings and weird cravings, too.

   Cycles is free for download, with multiple levels of premium access. The extra functions will allow you to connect with your partners through partner connect, get tailored predictions on upcoming changes to your body, and set up customized reminders for birth control, fertile days or periods.

9. Glow

   Before the aforementioned Eve, there was Glow—a tried-and-true period app backed by experts like Sheeva Talebian, MD, a board-certified reproductive endocrinologist at CCRM in New York and a Women’s Health advisory board member, who considers it to be one of the most useful period apps on the market because of all of the data points it collects. Glow allows you to track 40 different health signals including but not limited to sexual activity and body basal temperature, all through its easy daily log.

   Not only can it help you avoid or attempt pregnancy, but it can also help those who are undergoing fertility treatments through their online communities and accessible resources, says Alyssa Dweck, MD, an ob-gyn in Westchester County, New York.

   This app is free, but just like Eve by glow, you will need to upgrade to unlock access to premium content, comparative insights, a custom profile, premium support, and private messaging options.

10. Cycle Tracking

    These days it seems like you can do just about anything and everything from your…wrist. That includes tracking all things menstruation thanks to the new Cycle Tracking app for the Apple Watch. Available through the iPhone Health app that’s already built into the phone, Cycle Tracking gives you the ability to log info related to your cycle, including flow level, symptoms like cramps and mood changes, and basal body temp if you’re looking to get pregnant.

    “Its unique ability to log data through the Apple Watch, which improves the accuracy of data input,” notes Dr. Shah. Plus, you can opt in for notifications on your watch screen that alert you to when your next predicated period is on its way and when you’re in your fertile window (a big win for those trying to conceive).

11. My Calendar: Period Tracker

    Described as “sophisticated” and “elegant” by Dr. Dweck, this app allows you to customize everything from its watercolor theme to the style of your period reminders as either personal (“your period is due on…”) or discreet (“upcoming event…”).

    Taking birth control? You can finally shut off that daily phone alarm and just schedule pill reminders through the app as well. Dr. Dweck also compliments the app for its ability to be password-protected to ensure that your info remains private.

    This one is completely free, but if you prefer to access premium features, you can opt for a monthly or yearly paid subscription.