How we calculate

Astronomical engine

Positions come from astronomy-engine (MIT licence), which models the Sun, Moon and planets with an accuracy of about one arcminute. Positions are geocentric and apparent (corrected for light-time and aberration) and expressed in ecliptic longitude of date. Our automated test suite compares planets and house cusps with Swiss Ephemeris reference values for dates from 1900 to 2050; all agree to within one arcminute.

Western astrology

• Zodiac: tropical (0° Aries = March equinox).
• Houses: Placidus by default; Whole Sign and Equal are available. Placidus is undefined near the polar circles, so above about 66° latitude we switch to Whole Sign and say so.
• Lunar node: true (osculating) node.
• Aspects: conjunction, sextile, square, trine and opposition, with orbs of 5–8° (wider for the Sun and Moon).

Vedic astrology

• Zodiac: sidereal, using the Lahiri (Chitrapaksha) ayanamsa: 23.857092° at J2000, advanced with IAU 2006 precession and corrected for nutation. It matches Swiss Ephemeris to within 2 arcseconds in our tests.
• Houses: Whole Sign from the Lagna.
• Rahu/Ketu: mean node.
• Vimshottari Dasha: 120-year cycle from the Moon’s nakshatra, with years of 365.25 days.
• Panchang: tithi, nakshatra, yoga and karana prevailing at local sunrise, with end times found by numerical search.

Time and place

Birth places come from the GeoNames database (CC BY 4.0), with each city’s official time zone. Local birth time is converted to Universal Time with the IANA time-zone database, including historical daylight saving. If a time didn’t exist (clocks went forward) or happened twice (clocks went back), we tell you what we assumed.

Unknown birth time

Without a birth time we calculate for 12:00 noon local time, omit the Rising sign, Midheaven and houses, and warn you if the Moon changed sign that day.

Horoscopes

General horoscopes use solar houses: your Sun sign is the first house and each planet’s real position falls into one of the twelve life areas. A rule-based composer writes the reading from those placements and the period’s lunations, eclipses, retrograde stations and sign changes. An optional AI writer may polish the wording; its output is rejected if it mentions any placement not in the calculated data. Readings appear only once their date has begun in your time zone, and editors can review them before publication.

Limits

Astrology is not a scientifically validated way to predict events or personality. Compatibility scores are traditional, not statistical. Please read our content as an invitation to reflect. See also the FAQ.