YES there is an APP for that

mmpleaser

FDA approved the use of this APP to do birth control.
As long as anyone is using protective device, probably no need for it.
On the other hand, if one needs to have a young one soon,  this could plan your effort to conceive too.

As follows :

An easy to use mobile app as an effective method of contraception. Measure your temperature, enter it into the app and know exactly when you need to use protection.
Natural Cycles
What is Natural Cycles?
Natural Cycles is an effective method of contraception. And so much more. It's the app that gives you the knowledge to get to know your body and truly understand how your cycle works. It's protection with more sexual freedom - minus the side effects.
Natural Cycles
How does it work?
Every cycle is different but the thing is you can only get pregnant on up to 6 days in one cycle. We find those days for you. All you need to do is measure your temperature in the morning, enter it into the app and it will give you a red or a green day depending on whether you need to use protection.
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Natural Cycles
Can I have sex without protection?
Yes, on a green day. You cannot get pregnant as you are not fertile. Natural Cycles is backed by a unique algorithm that takes your temperature and many other factors like sperm survival, temperature fluctuations and cycle irregularities into account. It not only detects ovulation, fertility and the different stages of your cycle, it also calculates accurate predictions for upcoming cycles. Keep in mind that Natural Cycles does not protect against Sexually Transmitted Infections (STIs) in any way.
Natural Cycles
When do I need to use protection?
You should use protection or abstain on a red day, as there may be a risk of pregnancy. This is necessary for Natural Cycles to be an effective contraceptive. Keep in mind that it will take at least a couple of weeks for it to get to know your unique cycle. So you can expect more red days in the beginning, but once the app has detected your ovulation you are likely to get more green days.
Natural Cycles
Is it effective?
Yes. Natural Cycles' effectiveness is based on clinical research which makes it comparable to other methods. Choosing a contraceptive is such a personal thing. We get that. It's all about finding what is right for you and what method suits your lifestyle. So we recommend doing research and reading up on effectiveness, how it works and possible side effects.
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Ahdon

I wouldn't trust an app.

rocus5

But what if the app is wrong? Would they be held liable?

Zangcong

I heard this app is pretty accurate. A quick look at it in the play store returns high ratings, but do you trust the woman enough to believe it's her "safe" day?