The human body has a tiny quirk that many of us can live our whole lives without noticing: Body temperature ticks up by about half a degree after you ovulate, and decreases again around when your period begins. If you don’t personally ovulate, you probably don’t care. If you do, this fact can be enormously helpful in planning (or attempting to avoid) pregnancy. And Oura, the ring-shaped wearable best known as a sleep tracker, can now use it (along with other data) to predict your period.
I remember tracking my temperature when I was trying to conceive my first baby. Back then, you needed to buy a special thermometer at the drugstore that had an extra decimal place (so you’re not just 98.6F, but, say, 98.62F). You had to make sure to take your temperature first thing in the morning, when it’s most consistent, and always at the same time. And if you kept track in a notebook or on a special fertility-tracking website, you would be able to pinpoint when you ovulated, to within about a day.
You’re most likely to get pregnant in the last few days before ovulation, so knowing when that time comes every month is extremely helpful. And if you’d rather not get pregnant, temperature-based fertility awareness can help with that too — although, as you might guess, it’s not as effective as IUDs, oral contraceptives, or barrier methods like condoms. (Planned Parenthood has more info on this method here.)
When I first heard about how the Oura ring uses skin temperature as one of the factors that determine your “readiness,” I wondered if this meant that ovulation could throw off the scores. And that was true, at least at first — but then the company realised that temperature tracking could be valuable to wearers who ovulate. Not only might you track your temperature if you’re interested in getting pregnant, it’s also a good way of knowing where you are in your cycle.
If you get your period every four weeks, ovulation usually occurs right in the middle, about two weeks after your period starts. If your cycle is longer, usually the first half will be longer — say, three weeks from period to ovulation but then two weeks from ovulation to your next period.
What the Oura app does
There are other gadgets out there that track temperature changes for fertility, like the Ava wristband. Oura isn’t geared toward baby-making, specifically, but the company announced that the new version of their ring will include a period prediction feature in its app. The old ring will still let you view your temperature and tag days as period days, but the new one adds prediction algorithms.
(Importantly if you have an Oura ring or if you’re considering buying one, the company just changed their business model. Instead of buying the ring and getting its functionality for free — in contrast to Whoop, which gives you the tech for free and then charges for a subscription — Oura is now charging for the ring and planning to charge for a subscription. They’re offering deals right now to upgrade and get a lifetime subscription if you already have a ring, and they’re including a 6-month membership for new customers. If you plan to stick with your older model, it will still keep working as before. Gizmodo has more on the new ring and its features here.)
According to the company’s studies, including this one published last year, the ring is able to pick up on changes in temperature and heart rate variability (two things that it measures anyway in the course of sleep and health tracking) that predict the hormone surge that occurs around ovulation.
Period prediction will be available in iOS right away, the company says, and in Android shortly afterward. To set it up, you’ll turn it on in settings (or from a card that appears on your home screen), and then you’ll answer some questions about how long and how regular your cycles tend to be. After that, the ring will track your temperature and you’ll let it know every time your period starts. Here’s the company’s guide to the new feature.
It takes about two months to start getting accurate predictions, and then the app will be able to tell you each month when it expects your period. You’ll get an estimate 30 days out, a reminder six days before, and a reminder the day before.
The company has a disclaimer that, while the feature should work on cycles of all lengths, they don’t expect it to be accurate if you use hormonal birth control, have an IUD, or use hormone replacement therapy, since you won’t necessarily have the changes in temperature that it’s expecting.