Free birth chart calculator.

A birth chart, also called a natal chart, is a map of the sky at the moment and place you were born: where each planet stood along the zodiac, which sign was rising on the eastern horizon, and how the sky divided into twelve houses from that spot on Earth.

natalGPS converts your local birth time to universal time with the historical rules for your birthplace, including daylight saving as it was in that year, then asks the Swiss Ephemeris for the apparent geocentric position of every body. The Ascendant, Midheaven and house cusps follow from the exact time and coordinates, which is why the time matters so much: the Ascendant moves about one degree every four minutes.

If your birth time is unknown, choose that option and the calculator uses noon at your birthplace and leaves houses and angles out rather than guessing them.

The names differ, the calculation does not. Whatever you call it, the chart holds the same ten planets, the nodes, Chiron, twelve houses and the aspects between them. natalGPS shows all of it in one view and keeps the chart in your account as a profile, so you can return to it, compare it with a partner’s, run transits against it or map it across the world.

Written reports turn the geometry into language. Each report is generated from your own placements, houses and aspects and is framed as reflection rather than prediction.

• General report: the shape of the whole chart
• Relationship, Career, Money and Health reports by life area
• Chart summary and calculation details, including the exact UTC instant and time-zone rules used

A natal chart has four layers, and reading it means holding them together. Planets are the what: the Sun is your identity, the Moon your needs, Mercury your mind, Venus your affections, Mars your drive, and so on out to Pluto. Signs are the how: the style each planet works in. Houses are the where: the area of life in which it plays out. Aspects are the relationships between planets, the angles that make two of them cooperate, argue or reinforce each other.

natalGPS draws all four layers on one wheel and lists them in the placement and aspect tables beside it, so a beginner can start with the big three and a practitioner can go straight to the tight squares.

• Ten planets plus the North Node and Chiron, each with sign, degree and house
• Twelve signs of the tropical or sidereal zodiac
• Twelve houses from any of six house systems
• Conjunctions, sextiles, squares, trines and oppositions within your orb

Start with the big three: the Sun sign for identity, the Moon sign for emotional life, the rising sign for how you meet the world. Then find the chart ruler, the planet that rules your rising sign, and see where it sits. Next read the planets house by house, because a Venus in the tenth house lives a different life from a Venus in the fourth. Then look at the tightest aspects, the ones within a degree or two, which describe your recurring themes. Finally step back and look at the pattern: clusters of planets, empty halves, the balance of elements. natalGPS shows the orb of every aspect so the tight ones are easy to find.

House systems divide the sky above your birthplace into twelve parts, and they disagree about how. Placidus, the most common in Western astrology, divides the time a point takes to rise and culminate. Whole Sign gives each sign one house, starting with the rising sign. Equal cuts twelve 30° houses from the Ascendant. Koch, Regiomontanus and Campanus are further quadrant systems with their own geometry. Planets near a house cusp can change house between systems, which is why natalGPS lets you switch systems in one click and recalculates the wheel and the tables together. At far northern or southern latitudes the time-based systems break down, and natalGPS tells you to use Whole Sign or Equal.

The tropical zodiac, used by most Western astrologers, starts Aries at the spring equinox. The sidereal zodiac, used in Vedic and some Western traditions, anchors the signs to the stars; the two have drifted about 24° apart, so a tropical Aries Sun is often a sidereal Pisces Sun. natalGPS calculates both, with the Lahiri or Fagan–Bradley ayanamsa for sidereal charts, from the same birth data.

A newspaper horoscope uses one fact about you, the Sun sign, and writes for a twelfth of humanity. A birth chart uses the whole sky at your exact minute and place, which is why two people with the same Sun sign can have almost nothing else in common. Free birth chart calculators exist in many places; what sets natalGPS apart is that the same chart then feeds transits, astrocartography and synastry, and that every number can be checked against the ephemeris.