Which house system is correct?

None is proven correct. They are different traditions. Use the same one when you compare.

My Sun sign differs between apps. Why?

If you were born on a day the Sun changed signs, the answer depends on the time. Or one app may be using the Vedic zodiac.

Can two apps match on the chart and still disagree?

Yes. The chart is a calculation, the reading is interpretation.

Does a different result mean an app is broken?

Not on its own. Check the birth data and settings first.

Why do astrology apps give different results?

Apps can disagree for two different reasons. The chart itself can differ, because of different birth data, zodiac, ayanamsa or house system. Or the chart matches and only the reading differs, because interpretation is a choice. The first can be checked and fixed. The second is opinion, and no app's reading is proven.

Is it the chart or the reading?

Start here, because the fix is different.

Open your chart in each app and write down three things: your Sun sign, Moon sign and rising sign, with their degrees if the app shows them. Matching these three is a first check. Then compare the other planets' degrees, the house placements and the settings. Only when all of that matches is the difference purely in how they read it. If anything doesn't match, one of the reasons below is the cause.

Why would two charts not match?

1. Different birth details. A typo in the time, a city with the same name in another country, or AM and PM swapped will move the fast parts of the chart. The rising sign changes about every two hours on average, faster or slower depending on the sign and your latitude, so a small time error can change it. (The Astrology Podcast)

2. Time zones. A calculator has to turn your local birth time into universal time, using the time zone and any daylight saving rule in force at that place on that date. If a tool gets this wrong, the chart can be off by an hour.

3. Western or Vedic zodiac. Western astrology uses the tropical zodiac and Vedic uses the sidereal one. They are now about 24 degrees apart, so many placements move back one sign in a Vedic chart. (Kerykeion)

4. Different ayanamsas. Vedic tools don't all use the same value for that gap, and ayanamsas can differ by more than a degree. That can change a placement near a sign boundary.

5. Different house systems. Placidus, Whole Sign, Equal and others divide the chart differently. Kerykeion's guide notes that "When a planet falls near a sign boundary, it may be in different houses depending on the system used." (Kerykeion) The same guide says Placidus becomes "increasingly distorted" at high latitudes.

6. A guessed chart. A chat AI that is not running a real calculation can produce positions that look plausible and are wrong.

Why would two readings differ when the chart is the same?

Because interpretation is not calculation. Two astrologers looking at the same chart can stress different placements, use different traditions and write in different styles. An app's reading reflects the choices of whoever wrote its text or its AI instructions.

Daily horoscopes add another layer. Some are written for a whole Sun sign, so they are the same for everyone born in that month. Others use your full chart. Those two can say very different things.

None of these readings has been shown to predict events. So when two readings disagree, it doesn't mean one is broken. It means they are two interpretations, and neither is a measurement.

How do I find out which chart is right?

Confirm your birth date, time and place, ideally from a birth certificate.
Run the same details through a free calculator such as Astro.com.
Match the settings: the same zodiac, the same house system, and for Vedic charts the same ayanamsa.
Compare the Sun, Moon and rising sign, with degrees. If an app still disagrees with the calculator, check its settings or its time zone handling.

What does this look like with two real apps?

Maya was born at 7:40 in the morning. App A says she has a Gemini rising. App B says Taurus rising, and puts her Venus in a different house.

She checks App B's settings: it is on a Vedic chart. Switching it to Western, the rising sign matches App A, but Venus still sits in a different house. App A uses Placidus and App B uses Whole Sign, and her Venus sits near the edge of a house. Once she sets both to the same house system, the charts match. Their daily readings still differ, and that part is just two different writers.

How does Mystogian calculate charts?

Mystogian calculates your chart with astronomy code on our server, from your birth date, time and place, and the AI never calculates planet positions. You can switch between the Western (tropical) and Vedic (sidereal) chart. Readings do use AI.

FAQ

Which house system is correct?: None is proven correct. They are different traditions. Use the same one when you compare.
My Sun sign differs between apps. Why?: If you were born on a day the Sun changed signs, the answer depends on the time. Or one app may be using the Vedic zodiac.
Can two apps match on the chart and still disagree?: Yes. The chart is a calculation, the reading is interpretation.
Does a different result mean an app is broken?: Not on its own. Check the birth data and settings first.

Sources

The Astrology Podcast, "How to read a natal chart with no birth time": https://theastrologypodcast.com/2020/09/08/how-to-read-a-natal-chart-with-no-birth-time
Kerykeion, "Western vs Vedic astrology": https://kerykeion.net/content/learn-astrology/guide-western-vs-vedic
Kerykeion, "Placidus vs Whole Sign": https://kerykeion.net/content/learn-astrology/guide-placidus-vs-whole-sign
Astro.com free chart calculator: https://www.astro.com