Free birth chart calculator
Enter a birth date, time and place to get the full natal chart: planetary positions to the arcminute, house cusps in eleven systems, and nine aspect types, the five majors and four minors. The positions come from the same calculation engine that powers Astrolize for macOS, verified against JPL Horizons. Nothing you enter is stored.
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 across 1900 to 2050, planetary longitudes agree to better than 2.3 arcseconds and the Moon to better than 15 arcseconds. Charts are read at arcminute precision, so the calculated positions are exact for chart work.
Questions about birth charts
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?
Tick "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 across 1900 to 2050: planetary longitudes agree to better than 2.3 arcseconds and the Moon to better than 15 arcseconds. At the arcminute precision charts are read in, that is exact.
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. The shareable link keeps the birth details in your browser address bar only.
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, and configurable per-aspect orbs.
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.
Get Astrolize on the Mac App StorePlace search data by GeoNames (geonames.org), licensed CC BY 4.0. Map geometry by Natural Earth (naturalearthdata.com), public domain.