Calculator Methodology

How we compute placements, ascendants and moon signs

At a glance

How accurate are My Zodiac AI's free calculators?

Our calculators use astronomical algorithms from Jean Meeus and data aligned with Swiss Ephemeris. Sun and Moon sign calculations are accurate to a fraction of a degree; rising sign accuracy depends on your exact birth time and city.

  • Sun and Moon sign calculations are accurate to a fraction of a degree.
  • Rising sign accuracy depends on an exact birth time and city.
  • We use the same astronomical algorithms behind Swiss Ephemeris.

Ephemeris and astronomical source

We implement the core algorithms from Jean Meeus, Astronomical Algorithms, 2nd edition. This includes solar theory (chapter 25), lunar periodic terms (chapter 47), obliquity, sidereal time and planetary mean elements. The results are cross-checked against Swiss Ephemeris values to ensure consistency.

House and zodiac system

Calculations use the tropical zodiac, aligned with the seasons and the vernal equinox. House cusps are not required for Sun, Moon or rising sign calculations; if a full chart is generated, Placidus is the default house system.

Time zones, daylight saving and historical time

We use the IANA time zone database through the Intl API. Birth date and time are converted from local civil time to Universal Time before the ephemeris is evaluated. Historical daylight saving and war-time changes are handled by the browser or server Intl implementation.

Rising sign and birth time uncertainty

The Ascendant changes roughly every two hours as the Earth rotates. Without an exact birth time the rising sign cannot be determined reliably. We always show a clear warning when the birth time is missing or approximate.

Privacy and data handling

Free calculator inputs are used only to produce the result and are not stored on our servers. No birth data is retained after the response is sent. See our full Privacy Policy for more details.

Sources

  • Meeus, Jean. Astronomical Algorithms, 2nd edition. Willmann-Bell, 1998.
  • Swiss Ephemeris, Astrodienst. https://www.astro.com/swisseph/

Methodology FAQ

Are these calculators free?

Yes. All calculators on this page are free to use. No email or payment is required for the basic calculations.

Do I need an account?

No. You can use the calculators without creating an account. We do not store your birth details.

Why does the rising sign need my birth time?

The Ascendant is the point on the eastern horizon at birth. Because the Earth rotates once every 24 hours, the Ascendant moves through all 12 signs in a day, changing roughly every two hours.

Can I use these results instead of a professional astrologer?

Our calculators provide accurate astronomical data, but astrology is entertainment and reflection, not deterministic advice. For major life decisions, consult a qualified professional.

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