Is your birth data safe in an astrology app?
Published 10 August 2026 by Pacefyx, Inc. We make Undersky, an astrology app, so we have a stake in this. Everything below can be checked without taking our word for it.
It depends on one thing: whether the app keeps your birth details on your phone, or sends them to a company. You can find out in about thirty seconds, before you install anything.
Why does birth data matter more than other app data?
You can change a password. You cannot change where and when you were born. Those three details stay true about you for life, and together they point at one person quite precisely.
What gets built on top of them is the personal part. An astrology app ends up holding who you are dating, who your family is, what you are worried about, and what you are hoping for. Most apps know what you clicked. An astrology app knows what you are afraid of.
What happens to your birth data if the company is sold?
Whatever a company collected is usually part of what a buyer gets. Apps are bought and sold like anything else, and you cannot know at sign-up who will own the app in five years.
Co-Star was bought by Midjourney in 2026. That is not a knock on either of them. It is just what happens to companies, and it is the clearest example of why "do you trust this company" is a weaker question than it looks.
If a company never received your data, they cannot sell it. Nobody can buy it. Not even by buying the whole company.
That is the whole argument for keeping this kind of thing on your own phone. It is not a promise about how nice a company intends to be. It is about what is possible.
How do you check an astrology app's privacy yourself?
Open the app's page in the store and read the privacy section, which is what the developer told Apple or Google about their own app. It takes about thirty seconds, and it is better evidence than anything on a marketing site, including this one.
- Find App Privacy on the App Store, or Data safety on Google Play.
- Read Data Used to Track You and Data Linked to You. Those two matter most.
- An app that collects nothing shows one line: Data Not Collected.
- Check whether it needs an account. An account means a copy of you on someone else's computer.
- Try it with the internet off. An app that still draws your chart is doing the work on your phone.
The thing the labels will not tell you
There is no label category for "this app sends your reading to an outside service to be written." So a privacy label can look modest whether the app does that or not.
Some astrology apps do say in their privacy policy that they send your chart or your questions to an outside company to generate the text. If that matters to you, read the policy and look for named third parties. The internet-off test is the quickest check: an app that needs a connection to write your reading is sending something somewhere.
What does a private astrology app actually look like?
No account, no sign-up, and it works with the internet turned off. Those three together are hard to fake, because an app cannot secretly phone home if it still works on a plane.
Undersky is built that way. Your chart is worked out on your phone, there is no server of ours, and the App Store privacy label says "Data Not Collected". Your birth data is worth something, and we think it is worth the most to you. We will not sell it, and cannot sell it, by design.
A privacy promise with no limits is just marketing, so here are ours. Your data stays on your phone and we never collect it. If you back up your phone, that backup is yours and can include the app's data, which is how you move to a new phone. If you share a reading, that copy goes where you send it. If you email us for help, we have whatever you wrote.
The same is true of our other two apps, Muhura for Vedic astrology and Gilsung for Four Pillars and saju.
Common questions
Is it safe to give an astrology app your birth time?
It depends on whether the app keeps that time on your phone or sends it to a company. Your birth date, time and place cannot be changed later, so it is worth thirty seconds of checking before you type it in.
Do astrology apps sell your data?
Some collect a lot and some collect nothing, and the store privacy label is where you find out for any specific app. Read Data Used to Track You and Data Linked to You on its store page rather than relying on what any article says, including this one.
Does an astrology app need your exact birth time?
It needs it for your rising sign and your houses, which change every few minutes. It does not need it for your sun sign or most planet positions. An app that works things out on your phone can use your exact time without that time going anywhere.
Can I use an astrology app without an account?
Yes, though most of the well-known ones ask for one. Undersky has no account and no sign-up. If an app requires an account, your details are on its servers by definition.