Scroll through your phone and there’s a good chance you have a few apps for tracking the details of your life: What you ate, how far you ran, how well you slept or whether you stayed within your monthly budget.

If you’re thinking of having a baby — or trying to avoid a pregnancy — you might need to make room for one or two more of these agents of accountability. Thanks to the popularity of data-driven apps, there’s a growing market for programs designed specifically for family planning, including one that’s now being regulated as a medical device.

Natural Cycles, an app designed by Swedish physicist Elina Berglund, tracks your menstrual cycle and symptoms to determine when you are most or least fertile. The app uses the basics of natural family planning, which is the method of foregoing birth control options such as the pill, condoms or other options.

Users must purchase a thermometer and measure basal body temperature each day. After buying a subscription for the app and entering that data and some information about your cycle, the app “learns” and does a better job of synthesizing those numbers. It can then predict the small window of time you’re most likely to become pregnant. The app then let’s you know if it’s a “red” or “green” day based on fertility levels.

Dr. Eric Lantzman, co-director of the Allegheny Health Network’s Division of Family Planning, says the app can be a useful tool, as long as you’re the type of person who is interested in collecting data and organized enough to keep it up.

“People are really interested in learning more data about themselves and everything around them, and that’s what is making this a hit,” he says.

The makers of Natural Cycles say, based on a clinical study, the success of the app depends on the accuracy of the algorithm, as well as the behavior of the users. Lantzman seriously cautions against seeing it or any app as foolproof for preventing pregnancy. Other reasons for failure of the app in those tests, he says, were attributed to forgetting to check the app, ignoring the app or failing to provide a backup method of contraception.

Lantzman says if people are serious about preventing pregnancy and willing to use other options, they should use the app as a supplement, not the first line of defense. It’s also not a great option for women with irregular menstrual cycles.

“There are much, much more effective birth control and contraception options, like long-acting reversible contraception, intrauterine devices or progesterone (implants),” he says.

And for those using the daily pill, Lantzman recommends an app called Bedsider, which provides daily reminders that combine sexual health tips with a bit of humor.

While the apps come with another downside — they’re not covered by insurance — Lantzman says they provide an important lesson for users: Many women are unaware of the ins and outs of their own menstrual cycles and fertility, but tracking the small, daily details can add up to a much broader understanding.

“You can look at a day, a week, a month and you can see a pattern of what’s going on,” he says.