A free tool from Astrolize
Free birth chart calculator
Your natal chart in seconds: every planet, house and aspect, calculated by the engine behind Astrolize for Mac and measured against JPL Horizons. Free, no account, nothing stored.
- Measured against JPL Horizons
- 11 house systems
- Nothing stored
Reading guide
How to read your birth chart
A natal chart is a map of the sky at the moment and place of birth. Read it in four layers, from the broadest summary to the finest detail.
The Big Three
Sun, Moon and Rising are the quickest summary of a chart: the Sun for identity and will, the Moon for feelings and needs, the Rising sign (the Ascendant) for how you meet the world.
Planets in signs
Each planet stands for one function, and the sign it occupies colours how that function works. The degree places it within the sign; ℞ marks a planet that appeared to move backwards.
Houses
Twelve houses divide the sky around the birth place into areas of life. They turn once a day, so they need an exact birth time; without one they are left out rather than guessed.
Aspects
Aspects are angles between planets. Squares and oppositions, drawn in red, mark tension and drive; trines and sextiles, drawn in blue, mark ease. The smaller the orb, the stronger the link.
Precision
How the chart is computed
The birth time you enter is interpreted in the birth place's own timezone with the offset that was actually in force on that date, including historical daylight saving quirks; ambiguous clock readings around a transition are resolved the same way the Mac app resolves them. The instant is then handed to the Astrolize calculation engine, which computes apparent geocentric positions from the VSOP87 planetary theory and a high-order lunar series, derives the house cusps for the system you chose, and detects aspects between all thirteen bodies.
Measured against JPL Horizons, the largest sampled longitude difference is 3.36 arcseconds for Pluto across eleven dates from 1900 to 2099, and 9.26 arcseconds for the Moon across nine dates from 1900 to 2050. These are sampled measurements, not guarantees for every date.
- Pluto, largest sampled gap to JPL Horizons, eleven dates 1900 to 2099
- 3.36″
- Moon, largest sampled gap to JPL Horizons, nine dates 1900 to 2050
- 9.26″
- House systems, the same set as Astrolize for Mac
- 11
- Bodies, with every aspect between them detected
- 13
Questions
Questions about birth charts
What the calculator needs, what it does with your data, and how far its numbers can be trusted.
What do I need to calculate a birth chart?
Three things: the birth date, the birth time as it was read off a local clock, and the birth place. Type a city and the atlas fills the coordinates and the historically correct timezone, including daylight saving rules of the era.
What if I do not know my birth time?
Turn on "I do not know the birth time" and the chart is computed for 12:00 noon local time. Planetary sign positions are usually still right, but houses, the Ascendant and the Midheaven need an exact time, so they are left out. The Moon moves about 13 degrees a day, so its position can be off by up to about 7 degrees.
How accurate are the positions?
Every position comes from the same calculation engine as Astrolize for macOS. Measured against JPL Horizons, the largest sampled longitude difference is 3.36 arcseconds for Pluto across eleven dates from 1900 to 2099, and 9.26 arcseconds for the Moon across nine dates from 1900 to 2050. These are sampled measurements, not guarantees for every date.
Which house systems can I use?
All 11 systems the Mac app ships: Placidus (the default), Koch, Whole Sign, Equal, Campanus, Regiomontanus, Porphyry, Morinus, Topocentric, Meridian and Alcabitius.
Is my birth data stored?
No. The chart is computed in memory on our own server and returned to you; nothing you enter is saved, logged or sent to any third party. Nothing is put in your browser address bar.
Does the calculator use the tropical or the sidereal zodiac?
The web calculator uses the tropical zodiac. Astrolize for macOS also offers sidereal zodiacs, heliocentric and topocentric coordinates.
Astrolize for Mac
Take the chart further on your Mac
Astrolize for macOS keeps your charts in a local library and adds transits, progressions, returns, synastry and composites, sidereal zodiacs, interpretations and print-ready reports, all offline and without an account.
- Written interpretations
- Transits, progressions and returns
- Synastry and composites
- Print-ready reports
Place search data by GeoNames (geonames.org), licensed CC BY 4.0. Map geometry by Natural Earth (naturalearthdata.com), public domain.