Is your birth data safe in a BaZi or saju app?
Published 10 August 2026 by Pacefyx, Inc. We make Gilsung, a Four Pillars 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. A Four Pillars app ends up holding who you are seeing, who your family is, what you are worried about and what you are hoping for. Most apps know what you tapped. A saju app knows what you are afraid of.
Who else's birth data is in your saju app?
A compatibility reading needs a second person's birth date, time and place, and that person never agreed to anything. Gunghap in Korean, 合婚 in Chinese, and it is one of the most-used features in the whole category.
So the honest way to read a privacy label on a Four Pillars app is to think about your partner, your parent or your child as well as yourself. You can decide to hand over your own permanent details. You cannot decide that for someone else.
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 a BaZi 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 a sign-in. A sign-in 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 chart to an outside service to be written up." So a privacy label can look modest whether the app does that or not.
If that matters to you, read the privacy policy and look for named outside companies. The internet-off test is the quickest check: an app that needs a connection to write your reading is sending something somewhere. In Chinese app stores some fortune apps have started advertising that they collect nothing, which is good for the whole category, and the label is still where you go to confirm it.
What does a paid reading from a person do with your data?
If an app connects you to a reader, your birth details and your question go to that service, because that is what the product is. There is no way to have a person read your chart without a person receiving your chart.
That is not a criticism. A lot of people specifically want a human reader, and the popular Korean and Chinese fortune apps are good at arranging it. It is simply a different trade, and it is worth making the trade knowingly rather than by accident.
What does a private BaZi 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 quietly phone home if it still works on a plane.
Gilsung is built that way. Your four pillars are 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.
Gilsung also has no fortune tellers, no per-minute billing, no coins, no hearts and no ads, so there is no second business quietly attached to the first. It sells no talismans, charms or remedies either, which means it never has a reason to make you worry.
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, Undersky for Western astrology and Muhura for Vedic astrology.
Common questions
Is it safe to give a saju 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 fortune 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.
Is there a saju app with no account?
Gilsung has no account, no sign-up and no phone number. If an app requires a sign-in, your birth details are on its servers by definition, which is not automatically bad but is worth knowing before you type them.
Does a BaZi app need my exact birth time?
It needs your exact time for the hour pillar, which changes every two hours and shifts again once true local solar time is applied. The year, month and day pillars do not need it. An app that works things out on your phone can use your exact time without that time going anywhere.