What the Zodiac Birth Chart Calculator does
This birth chart calculator draws your natal chart from your birth date, local time and birthplace: the Sun, Moon and eight planets by sign and degree, the ascendant and midheaven, twelve houses (whole-sign or equal), the major aspects between them, and a chart wheel you can print, with a table you can download as CSV or JSON. It offers the Western tropical zodiac and the sidereal zodiac with the Lahiri ayanamsa used for a Vedic kundli.
Every position is calculated in your browser from published algorithms - Jean Meeus for the Sun, Moon and sidereal time, Paul Schlyter's orbital elements with perturbation terms for the planets - and checked against NASA JPL Horizons. The page keeps the two kinds of information apart: where the planets were is astronomy, and you can check it; what a placement is said to mean is astrological tradition, and it is labelled as such.
How to use it
- Enter the birth date and local clock time. If you do not know the time, tick the box: the planets are drawn for noon and the houses are left out, because they depend on the time.
- Choose the birthplace from the list or type its latitude and longitude; the time zone follows the city, and can be changed.
- Pick the zodiac (Western tropical or Vedic sidereal) and the house system (whole sign or equal).
- Read the headline for your Sun, Moon and rising signs, then the wheel: signs around the outside, houses numbered inside, planets at their degrees and aspect lines across the middle.
- Use the planet table for exact degrees, house positions and retrograde motion, and the aspect table for the angles between planets and their orbs. Download the CSV or JSON to keep the numbers.
Reading the results
Each planet's row gives its sign and degree, its ecliptic longitude (0 to 360 degrees from 0 Aries), its house, and whether it was moving direct or retrograde as seen from Earth. The Sun and Moon are never retrograde.
With whole-sign houses, the whole rising sign is the first house, the next sign the second, and so on - the oldest system, and the usual one in Indian astrology. With equal houses each cusp is exactly 30 degrees from the ascendant degree.
An aspect is an angle between two points: conjunction 0, sextile 60, square 90, trine 120 and opposition 180 degrees, counted when the actual separation is within the orb (8 degrees for conjunctions, trines and oppositions, 7 for squares, 6 for sextiles). The orb column says how far from exact each one is.
Without a birth time the Moon could be up to about 6.5 degrees from the noon position, so aspects to the Moon are approximate and the page warns you if the Moon changed sign that day.
Worked example: a morning birth in Mumbai, 15 August 1990
06:30 India Standard Time is 01:00 UTC. The Sun's apparent longitude is 141.96 degrees: 141.96 - 120 = 21.96, so the Sun is at 21 deg 57' Leo. The Moon is at 70.28 degrees, 10 deg 16' Gemini.
The local sidereal time for 72.878 E is 3h 24m 15s, giving an ascendant of 143.56 degrees (23 deg 33' Leo) and a midheaven of 53.45 degrees (23 deg 27' Taurus). With whole-sign houses, Leo is the first house, so the Sun and Venus (1 deg 22' Leo) are in house 1 and the Moon in Gemini is in house 11.
Saturn at 289.90 degrees (19 deg 54' Capricorn), Uranus and Neptune were all retrograde. Mercury at 169.05 degrees and Saturn at 289.90 are 120.85 degrees apart - a trine with an orb of 0.85 degrees, listed in the aspect table.
Formulas and scoring rules
- Planet positions
heliocentric orbit from elements of date -> minus Earth's position -> light-time -> + aberration + nutationSchlyter's orbital elements with his Jupiter, Saturn and Uranus perturbation terms; Earth from the Meeus solar theory. Agreement with JPL Horizons is within about 2 arc-minutes.- Ascendant and midheaven
ASC = atan2(cos LST, -(sin LST cos e + tan lat sin e)); MC = atan2(sin LST, cos LST cos e)- Whole-sign houses
cusp n = 30 x floor(ASC / 30) + 30 x (n - 1)- Equal houses
cusp n = ASC + 30 x (n - 1)- Aspect
separation = |longitude A - longitude B| folded to 0..180; aspect if |separation - angle| <= orb- Retrograde
retrograde when the geocentric longitude decreases: (lambda(t + 0.05 d) - lambda(t - 0.05 d)) < 0
Why there is no Placidus option
Placidus and Koch houses divide time rather than the ecliptic, and they break down at high latitudes, where some houses become enormous and others vanish. Whole-sign and equal houses are defined everywhere outside the polar circles and are easy to check by hand, which is why this page uses them. If you work with a quadrant system, the planet longitudes in the CSV are the same in every house system; only the house numbers differ.
Tropical chart or kundli?
The Western chart measures signs from the March equinox; a Vedic kundli measures them from the stars, which are now about 24 degrees further on. Switching to sidereal subtracts the Lahiri ayanamsa from every position, so most planets move back by roughly one sign. The aspects do not change, because the angles between planets are the same in both zodiacs.
Limitations: what the result does not prove
- Accuracy is about 2 arc-minutes for the planets and much better for the Sun and Moon - more than enough for signs, houses and aspects, but not a substitute for an ephemeris when you need positions to the arc-second.
- Dates from 1900 to 2100 only; Pluto's series is valid to 2100.
- The ascendant and houses are undefined inside the polar circles, and only whole-sign and equal houses are offered.
- Interpretations are astrological tradition, not science. The chart is a picture of where things were in the sky, not evidence about personality, health or the future.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- NASA JPL Horizons - solar system ephemeris used to check positions - checked 19 Sep 2026
- Paul Schlyter - How to compute planetary positions
- NASA Eclipse Web Site - Delta T polynomial expressions
Frequently asked questions
What do I need to make a free birth chart?
Your birth date, the local time and the birthplace. The date alone gives the planets' signs; the time and place add the rising sign, the midheaven and the houses, and fix the Moon's position, which moves about half a degree an hour.
Is this a kundli chart?
Switch the zodiac to sidereal and keep whole-sign houses and you get the positions and houses a North or South Indian kundli is built from, with the Lahiri ayanamsa. The wheel itself is drawn in the round Western style rather than as a square kundli diagram.
What do the lines in the middle of the chart mean?
They are aspects - angles between two planets. Blue lines are trines and sextiles (dashed), red lines are squares and oppositions. Conjunctions are planets sitting together, so they appear in the aspect table rather than as a line.
Why is a planet marked R?
R means retrograde: seen from Earth the planet was moving backwards through the zodiac, an effect of Earth overtaking it or being overtaken in orbit. The table gives its daily motion so you can see how close it was to a station.
How accurate are the planet positions?
They are checked in the tests against NASA JPL Horizons at eight dates between 1912 and 2088: the Sun and Moon to within about 0.01 degrees and the planets to within about 2 arc-minutes, far smaller than any sign or house boundary question usually needs.
Which house system should I choose?
Whole-sign houses are the oldest system and standard in Indian astrology; equal houses start from the exact ascendant degree and are common in modern Western practice. Both are offered because both can be checked by hand; the planets' signs are the same either way.
Last reviewed by the A2Z.Tools team against the sources listed above.
