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About Clue

Here's why you can use period trackers for getting pregnant, but not for preventing it

Many period trackers out there show a fertility window or fertile days which can help you better understand the days when you are more likely to become pregnant if you have sex.

You can use Clue to track your cycle regularity, cycle length, basal body temperature (BBT), cervical fluid, and the results of ovulation tests to help give you a better idea of when you are most fertile.

While you can use Clue and other apps to help you understand your body and become pregnant faster, you can’t use them to avoid pregnancy. Why? For one, it’s extremely difficult to understand when you are fertile, and second,  it’s also hard to fully understand the risk you’re really taking especially when the app is unregulated. If you want to use an app for birth control, make sure it is certified and regulated as a medical device, for example by the FDA (in the US) or by the European regulatory authorities (in which case it will have a “CE” mark). 

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Download Clue to track your cycle length and changes.

  • Download the Clue app on the App Store
  • Download the Clue app on the Play Store


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Why can’t I use Clue as contraception?

Many apps show a window of time when you are considered fertile, however, the exact timing of ovulation is difficult to predict  and can vary cycle to cycle (1). For example, during one cycle you might ovulate on day 15, and on the next cycle, you could ovulate on day 13 (1).  There are many factors that affect when and if your ovulation window fluctuates which can include things like stress, illness, exercise, and diet (2). It’s untrue that you can only get pregnant on the day of ovulation, so you should always use some form of birth control if you don’t want to become pregnant.

Clue previously indicated a fertile window because we knew that some users found this helpful when trying to conceive. However, this was intended only as an estimated indication of your most fertile days. It wasn’t designed to assure that users could safely have unprotected sex outside of this period if they were trying to avoid pregnancy. We were concerned that some of our users misunderstood the fertile window’s purpose. 

Some apps have been developed with the goal of being used as birth control. They estimate and indicate days where they consider a user’s risk of pregnancy to be low, or high (3). To do this, they take into account the rules of certain Fertility Awareness Based Methods (FABM), cycle regularity, and sometimes measures including cervical fluid, basal body temperature, your period start dates, or a combination of two or more of these measurements depending on the method. 

In these methods, the block of time indicated as high risk needs to be considerably longer than a ~6-day fertile window, because no app can perfectly predict with 100% accuracy when your biological fertile window will occur. Apps have to add a significant “buffer” around their estimation in order to show you all the days where the risk of becoming pregnant is unacceptably high. Their ways of communicating risk levels to users also vary and are not one-size fits all solutions.

Please do not put yourself at an unknown risk of unintended pregnancy by using an app for contraception that has not been cleared by medical device regulators. An unintended pregnancy can be devastating, depending on your life circumstances and the stage of pregnancy when you find out. While no method of contraception is 100% effective, the reason that birth control is regulated in most countries is to make sure that its efficacy has been checked thoroughly by regulatory experts before it reaches users. It must be determined to be effective in a robust clinical study, and the company responsible for producing it is subject to strict oversight and quality control standards. In the US, the relevant authority is the Food and Drug Administration (FDA); in the EU, a regulated medical device carries the “CE” mark. Companies must advertise when they are regulated. If it is unclear, you can always ask them. 

If you are considering using an unregulated app as contraception, remember that apps that show you a fertile window for contraception without any regulatory oversight may not be based on science. They may show you predictions that have never been independently verified. They may be developed by companies that were never independently audited. If a pregnancy would be a bad thing in your life right now, how much do you care whether you are taking a 10%, 25%, or 70% risk of becoming pregnant? Would you buy your birth control pill from an unknown manufacturer on the internet? 

Is there still a way to learn about my fertility with Clue? 

Whether or not fertility is part of your life right now, our ongoing goal is to acknowledge, educate, and strive to include a wider audience. Although the fertility window will no longer be shown on your Clue app, you have the option of turning the approximated ovulation day on. Like the previously shown fertile window, the ovulation day is meant for users trying to get pregnant or for educational purposes only. It should not be used as a way to avoid pregnancy.

In addition to turning the estimated ovulation day on, the best way to understand when your body could be ovulating is to pay attention to other physical indicators such as:

  • Cervical fluid changes: eggy, wet, slippery, clear, stretchy (4)

  • Rise in basal body temperature (4)

  • Cervical changes (4)

  • Ovulation pain (4)

  • Ovulation bleeding (4)

  • Increased libido (5)

  • Breast tenderness (4)

  • Backaches / headaches (4)

  • Mood changes (6)

  • Energy level changes (may influence performance during exercise) (7)

  • Heightened sense of smell (8)

Tracking these changes in Clue can help you become more in tune with your body and give you better insight into when you are most likely to ovulate.

What does the ovulation day mean in Clue? 

Ovulation occurs when one of your ovaries releases an egg (1). The egg can be fertilized for up to 24 hours as it journeys through the fallopian tubes towards the uterus (9). Sperm can live inside the body for up to five days before ovulation (10), depending on the health of the sperm and the quality of the cervical fluid. This is why you can be “fertile” before ovulation occurs, and having sex almost a week ahead of ovulation can lead to pregnancy.

When the ovulation day is indicated in Clue, it’s just an estimate to show when your body could be ovulating based on the data you’ve tracked previously. You can continue to use the ovulation day indicator in the new cycle view. To turn it on, go to Menu, Settings, Ovulation and turn the toggle ‘on’. The potential ovulation day will show if you’ve tracked at least two cycles (two period start dates) with Clue. When the ovulation setting is turned off, your Cycle View screen will show a link that says "Learn about your cycle."

How is the ovulation day estimated in Clue?

Estimates for your day of ovulation are determined by counting backwards 14 days from your average cycle length. Clue may use a different value, if your BBT data or a "ovulation test pos." tag indicates otherwise. This means Clue's estimate of your actual day of ovulation improves at the end of each cycle.

Clue uses this method of counting backwards because counting forwards from the first day of your period is inaccurate for any person who has a cycle length different from 28 days.

Your predicted day of ovulation will look like this in the Clue app:

Screenshots of Clue's cycle view

So, if you have unprotected sex or use another form of insemination up to five days before ovulation, the sperm can live long enough to potentially fertilize the egg and pregnancy may result.  If the egg is not fertilized within this time, it passes out of your uterus with your period. 

Our goal is to continually improve our products by making them safer, more inclusive, and more educational for all users. We hope you enjoy and understand this new app update!

an image of 3 mobile screens of the Clue app

Download Clue to track your period and menstrual cycle.

  • Download the Clue app on the App Store
  • Download the Clue app on the Play Store


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