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Free calculator · Astrology

Birth Chart Calculator

Your birth chart shows where the Sun, the Moon and the planets stood at the moment of your birth, seen from your birthplace. The calculator works it out the way the UmbraLux app does: planets, Ascendant and MC to the arcminute, Placidus houses and the aspects between them.

Date of birth

As exact as you can, ideally from your birth certificate.

Your place is missing? Take the nearest town; a few kilometres hardly change the result.

The calculation runs in your browser. Your birth data is neither sent nor stored; only this device remembers your last entry. · Place data: GeoNames (CC BY 4.0)

How the birth chart is calculated

The calculator runs the same calculation as the UmbraLux app, in five steps:

  1. 1

    The birth moment in Universal Time

    Date and time are converted to Universal Time with the time zone of your birthplace on that day, summer time included.

  2. 2

    The planets in the zodiac

    For that moment the ephemeris gives the ecliptic longitude of the Sun, the Moon and the planets as seen from the Earth, in the tropical zodiac (0° Aries at the vernal equinox), with the true lunar node, Chiron and the mean Lilith (the Moon's mean apogee).

  3. 3

    Ascendant and MC

    Sidereal time and the latitude and longitude of the birthplace give the Ascendant, the degree of the zodiac rising in the east, and the MC, where the zodiac crosses the meridian (Midheaven).

  4. 4

    The Placidus houses

    Placidus divides the time each degree of the zodiac takes from rising to the Midheaven, and from the lower meridian to rising, into three equal parts; the degrees on those borders are the cusps of houses 11, 12, 2 and 3, the others lie opposite. Beyond the polar circles, where some degrees never rise, the calculator splits each quadrant into three equal arcs (Porphyry).

  5. 5

    The aspects

    Two points form an aspect when the angle between them is close to 0° (conjunction), 60° (sextile), 90° (square), 120° (trine) or 180° (opposition). The calculator allows 8° either way, 7° for the square and 6° for the sextile.

Example: 15 May 1990, 14:30, Berlin

14:30 in Berlin was 12:30 Universal Time (UTC+2). The Sun stood at 24°24′ Taurus in the 9th house, the Moon at 27°25′ Capricorn in the 5th. The Ascendant lay at 18°47′ Virgo, the MC at 15°09′ Gemini.

The closest aspect joins Jupiter and Uranus: an opposition with an orb of 0°22′. In all, the calculator finds 41 aspects between the planets, points and axes.

What the birth chart describes

Astrology reads the birth chart, also called the natal chart or radix, as a picture of a person's disposition: the Sun as the core, the Moon as the world of feeling, the Ascendant as the way of meeting the world. The houses place the planets in areas of life, the aspects describe how they work together.

The calculation is astronomical and exact; what it means is the teaching of astrology.

In the library

Questions about the birth chart

Which house system does the calculator use?

Placidus, like the UmbraLux app. Other systems (Koch, Whole Sign, equal houses) set the cusps differently, so a planet can fall into another house; its sign and degree stay the same. Beyond the polar circles the calculator uses Porphyry, as Placidus has no cusps there.

Can I calculate my birth chart without a birth time?

Partly. Without a time the Ascendant, the MC and the houses are missing: they move through the whole zodiac in 24 hours. The planets mostly stay in one sign all day; the calculator names the ones that change, with the time. In a sample of 2,000 days from 1940 to 2024, the Moon changed sign on 44 % of them, the other bodies and points together on 14 %.

How accurate is the calculator?

In 5,000 test charts from 1940 to 2024, at places between 60° south and 65° north, the planets lay within 20 arcseconds of a calculation on the Swiss Ephemeris, the Ascendant, the MC and the house cusps within one arcsecond. Of 50,000 planet placements none fell into another house and one into another sign: Saturn, one arcsecond past the border.

What does the ℞ in the table mean?

The planet was retrograde: seen from the Earth, it seemed to move backwards through the zodiac. The calculator marks it where the planet's longitude decreased at the birth.

Is my data stored?

No. The calculation runs in your browser; your date, time and place are neither sent nor stored. Only your device remembers your last entry, and you can delete it below the form.

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