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Why are some days “high risk” in Clue Birth Control?

How Clue Birth Control predicts which days are high risk for pregnancy

Top things to know

  • Clue Birth Control uses an evidence-based algorithm to determine which days are high risk for pregnancy 

  • To prevent pregnancy on high risk days, use a barrier method such as a condom every time you have sex that may result in pregnancy

  • Clue Birth Control uses the first period start date you enter to predict your high risk days

  • As you enter more period start dates, you’ll have fewer high risk days

  • The ovulation day in Clue Period Tracking mode is only an estimate, and shouldn’t be used to prevent pregnancy 

Prevent pregnancy by tracking your cycle with Clue Birth Control

  • Download the Clue app on the App Store
  • Download the Clue app on the Play Store
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Clue Birth Control is a new, digital form of birth control. It's not a pill, it's not inserted into your body and it is hormone free. And bonus—it doesn’t cause side effects. It's a mode in the Clue app that works by calculating which days of the menstrual cycle are high risk or low risk for pregnancy by predicting your window for ovulation. 

In order for Clue Birth Control to be effective, on high risk days you need to use a barrier method such as a condom every time you have sex that may result in pregnancy. 

Let’s dig into the definition of high risk days and how they make Clue Birth Control effective.

What are high risk days in Clue Birth Control?

Clue Birth Control calculates and displays your current pregnancy risk for each day of your cycle based on the period start dates you enter in the app. You should check Clue Birth Control before you have sex that may result in pregnancy. On days when the risk of pregnancy is high, you will see a message in an orange banner at the top of the screen: “Your risk of pregnancy today is high. Use protection.”

On high risk days, you must use a barrier method, such as a condom, to prevent pregnancy. 

Make sure to have a barrier method available to you to use during high risk days. That means making sure you have the appropriate size condoms that are not expired (condoms have an expiration date), melted, or damaged and that you use water-based lubricant that will not cause the condoms to rip or tear.

How does Clue Birth Control determine high risk days?

High risk days are determined after you enter the first day of your most recent period into the app. This triggers Clue Birth Control to detect the high risk days in your cycle. Your period start date is the first full day of menstrual flow. If you don’t remember your last period start date, wait until your next period starts and enter that date. You can use Clue Birth Control mode for contraception after you enter one period start date. For the first cycle, 16 days will be considered high risk. As you continue to enter period start dates, the Clue Birth Control algorithm can eventually narrow the number of high risk days to 11–13 days depending on your cycle lengths and variability. 

Why are there so many high risk days?

Ovulation needs to occur in order for a person to become pregnant. This is when the egg is released, allowing it to potentially become fertilized by sperm. Ovulation occurs near the middle of your cycle (1). In general, the highest probability of pregnancy occurs two days before ovulation (1). However, various factors can influence this, causing ovulation to vary a bit from cycle to cycle, making the timing of ovulation not exactly consistent between menstrual cycles (2, 3). 

This means that the number of days between menstruation and ovulation might be different each month, and can be difficult to predict. Clue Birth Control considers up to 16 days of the cycle high risk because these days have a high probability of pregnancy. Over time the number of high risk days can decrease as you enter your period start dates because the algorithm will be able to use your menstrual cycle patterns to make more personalized predictions.

Is the risk for pregnancy the same on every high risk day?

Because of the natural variability in ovulation, all days marked high risk in Clue Birth Control mode must be considered equal risk. For Clue Birth Control to be effective, you should use a barrier method such as a condom every time you have sex that may result in pregnancy on high risk days.

Are high risk days the same as the ovulation day in Clue Period Tracking mode?

The estimated ovulation day in the Clue Period Tracking mode cannot be used for contraception. It does not use the same sophisticated and clinically researched algorithm to determine ovulation as Clue Birth Control. The Clue Period Tracking mode was designed for people to use as a tool to track periods and experiences across menstrual cycles. This information helps people learn about their bodies.

The estimated ovulation day displayed in the Clue Period Tracking mode does not use the same algorithm as the Clue Birth Control mode. It is a scientific estimation of when you could be ovulating. The reason we include this estimation in Clue Period Tracking mode is because people may have experiences or symptoms around the time of ovulation that they wish to track. Having an estimate of the ovulation day can help pinpoint why some of these are occurring.

Preventing pregnancy with Clue Birth Control 

Clue Birth Control is 92% effective at preventing pregnancy with typical use and 97% effective with perfect use (4). To use Clue Birth Control effectively, it’s necessary to use a barrier method such as a condom every time you have sex that may result in pregnancy on a high risk day, no matter where the high risk day is in your cycle. To read more about Clue Birth Control and to learn if it’s a good fit for you, read this article on who Clue Birth Control is right for

For everything you need to know about Clue Birth Control, refer to our User Manual.

Clue Birth Control will be launched in the USA in 2022. We are excited to bring Clue Birth Control to other countries soon. This will take a little more time, but we’re on it.

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