Astrology Birth Chart Calculator

What does a birth chart show?

Most horoscope pages give you a Sun sign and stop: one line of a map with ten planets, twelve houses and four angles. A natal chart, or birth chart, records where every planet stood at the minute of birth, seen from the birthplace: its zodiac sign and its house, the part of the local sky it occupied. Date, clock time and coordinates fix that moment.

The astrology birth chart calculator above places the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto plus the North Node. The Ascendant (ASC), the degree rising in the east, and the Midheaven (MC), the degree at the top of the sky, frame the wheel. Sun, Moon and rising sign are the Big Three, the card you see first and, in my readings, the skeleton of the chart.

How do you read the four result tabs?

Chart is the wheel. Signs run counter-clockwise round the outer ring, tinted by element, with the Ascendant at nine o'clock. Gold lines are the axes, thin spokes the house cusps; centre lines are aspects: blue for sextiles and trines, red dashed for squares and oppositions, gold for conjunctions. Tap any glyph, house number or line for a one-line meaning.

Positions lists sign, degree and minute, house and R for retrograde, then ASC, MC and North Node; More points adds the Mean Node, Lilith (mean) and Part of Fortune, and House cusps the start of each house. Aspects is a grid with the orb in each cell and a list below, tightest first: an aspect within 1–2° speaks louder than one at 7°.

Analysis counts the ten planets by element (Fire, Earth, Air, Water) and modality (Cardinal, Fixed, Mutable); the dominant pair gives the Signature Sign. The prefilled example, 15 Jul 1990 at 14:30 in New York, has four planets in Earth and six in Cardinal signs: Capricorn. Ties go to the element of your Sun, then Moon, then Ascendant.

Worked example: Albert Einstein's birth chart

I test every chart program on the same birth first: Albert Einstein, 14 Mar 1879, 11:30, Ulm (48°24' N, 10°00' E), Rodden rating AA because the time comes from the birth record. Ulm kept local mean time then: 10° east × 4 minutes per degree = 40 minutes ahead of Universal Time.

The Big Three: Sun 23°30' Pisces in the 10th house, Moon 14°31' Sagittarius in the 6th, Cancer rising. Mercury, Saturn and Venus sit together in Aries, so with the Sun four planets fill the 10th house. The tightest aspects: Mercury conjunct Saturn (orb 1°02'), Sun sextile Pluto (1°13'), Moon square MC (1°41'). Fire and Earth tie at 4; the Pisces Sun cannot break the tie, the Sagittarius Moon does, and Fire plus Cardinal gives an Aries Signature Sign.

In Whole Sign houses the Sun moves to the 9th and Jupiter to the 8th; signs and degrees stay put. Read 11:30 as Berlin local mean time (UTC+0:53:28, what the time-zone database stores for Germany) and the Ascendant slips to 8°50' Cancer; hence the time line "Before standard time: local mean time of the birthplace (UTC+0:40)".

Why do birth time and time zone matter so much?

The sky turns once a day, so the Ascendant runs through all twelve signs in 24 hours: on average 1° every 4 minutes, a new rising sign about every two hours. In New York, Pisces and Aries rise in little over an hour, Leo to Scorpio in over two and a half each. Planet signs barely notice a wrong hour; angles and houses do.

The error I meet most is the wrong UTC offset. The prefilled New York chart is on summer time, UTC−4: 18:30 UT, Ascendant 6°56' Scorpio, MC 14°22' Leo. With standard time, UTC−5, you get 18°42' Scorpio and 29°47' Leo: one hour moves the Ascendant almost 12° and the MC over 15°, enough to shift houses. History adds traps: London kept UTC+1 all year between late 1968 and 1971, Berlin ran double summer time (UTC+3) in the summer of 1945, Kathmandu used +5:30 before its +5:45, Brazil has dropped summer time altogether.

The calculator reads those rules from the time-zone database in your browser and prints the result first: "New York: UTC−4:00 (summer time) → 18:30 UT on 15 Jul 1990". A time skipped or repeated at a clock change gets a warning and a choice in Edit. Enter the time exactly as written on the birth certificate. Village not among the 34,000 places? Type Latitude and Longitude: the zone of the nearest town is filled in, and Edit takes another zone or a fixed UTC offset.

Placidus, Whole Sign, Equal or Porphyry — which house system?

Houses divide the local sky, and astrologers have argued how for two thousand years. Signs, degrees and aspects are the same in every system; only house numbers change when you switch House system.

My advice: use Placidus to compare with books and other sites, look at Whole Sign when a planet sits a few degrees from a cusp, and keep one system for your notes. Beyond the polar circles Placidus can have no solution: for a birth in Tromsø (69.6° N) at noon on 21 Jun 1980 the calculator says so under the wheel and shows Porphyry instead of inventing cusps.

What if I don't know my birth time?

Tick Unknown time and the chart is cast for local noon. I would rather show less than guess: Ascendant, Midheaven, houses, Part of Fortune and aspects to the angles are hidden. Planet signs stay reliable, except a Moon that changes sign that day: it covers 12–15° in 24 hours, so you get its range, for 15 Jul 1990 in New York 18°35' Aries at midnight to 2°39' Taurus at 23:59. Rectification, timing a chart from life events, is work for an experienced astrologer; the guide to rising signs and birth times shows what you can do yourself.

Where do the numbers come from?

Every chart passes one chain in your browser: local clock time → UTC offset of the place on that date → Universal Time → ΔT (about −5 seconds in Einstein's day, over a minute now) → sidereal time and true obliquity → apparent geocentric longitudes on the ecliptic of the date, the convention Swiss Ephemeris prints. The zodiac is tropical; sidereal (Vedic) positions are about 24° lower.

Planets come from Astronomy Engine (MIT licence), built to stay within one arc minute of the US Naval Observatory's NOVAS. Against NASA JPL's DE440 ephemeris in twelve test charts the largest difference was 0.29' (Neptune). Minutes are truncated, as on astro.com. Towns come from GeoNames (CC BY 4.0), about 34,000 places; offsets from the IANA time-zone database. Dates run from 1800 to 2100. There is no Chiron: it needs a separate ephemeris.

Aspects and orbs used

Aspects are measured between the ten planets and to the ASC and MC when the time is known; minor aspects are left out so the grid stays readable. The Signature Sign comes from this square:

Saving and sharing charts from the astrology birth chart calculator

Download PNG, Print and Copy Data give you the chart as an image, on paper or as plain text. Share link packs the birth data after the # in the address, which browsers never send to a server, and Chart History keeps your last ten charts in this browser. Nothing is uploaded.

Going further: how to read your birth chart step by step, what your rising sign depends on and what each of the 12 houses rules. Astronomy is exact; the meanings are astrological tradition, for reflection — not predictions.