This astrology chart calculator uses precise astronomical computation (inspired by Kerykeion) to generate natal charts, synastry, composite charts, solar/lunar returns, and ephemeris timelines from birth data. Enter a date, time, and place of birth to receive a complete SVG chart showing planetary positions, house cusps, and aspect table, exportable as PNG or structured JSON. All calculations run inside the browser via WebAssembly — birth data never leaves your device.
How birth time accuracy affects your chart
Every 4 minutes of birth time error shifts the Ascendant by approximately 1 degree and moves all house cusps with it. If the exact time is unknown, tick the "birth time unknown" checkbox; the tool defaults to noon (12:00), the standard convention in astrology. In that case, planetary sign positions are still reliable, but house placements and the Ascendant are not — focus on the planetary and aspect analysis instead.
Zodiac system and house system pairings
Western astrology
- Zodiac: Tropical
- House system: Placidus (most widely used)
- Whole Sign is a good alternative at high latitudes where Placidus produces very unequal houses
Vedic astrology (Jyotish)
- Zodiac: Sidereal (Lahiri ayanamsa)
- House system: Whole Sign
- Planetary positions shift roughly 23–24 degrees compared to Tropical
Filling in the timezone field correctly
The timezone field expects an IANA timezone identifier such as America/New_York or Europe/London, not a raw UTC offset like UTC-5. Raw offsets cannot account for historical daylight saving changes. For birth dates before the 1970s, or in places that have shifted timezones multiple times, using an offset can introduce an error of one hour or more. The field pre-fills with your browser's current timezone — change it manually if the birthplace is in a different zone.
What each chart mode produces
Natal — single person's birth data; optionally overlays current transits.
Synastry — two birth charts side by side; highlights inter-chart aspects and compatibility.
Composite — a single chart computed from the midpoints of two people's planets; represents the relationship's combined dynamic.
Solar / Lunar Return — calculates the moment the Sun (yearly) or Moon (monthly) returns to its exact natal position, used for annual and monthly forecasting.
Ephemeris timeline — generates a table of planetary positions over a date range with a selectable step interval (day, hour, or minute); useful for tracking transits and retrograde periods.
Reading the aspect table
The Orb column shows how many degrees the current aspect deviates from exact. A smaller orb means a stronger influence. Applying aspects (planets moving toward exact angle) are generally considered more active than separating ones. Use the "major aspects only" filter to focus on conjunction, sextile, square, trine, and opposition while hiding minor aspects.
Exporting results
PNG export includes the full wheel chart with a dark footer showing tool attribution. JSON export contains all computed data in structured form — useful for feeding into external scripts or cross-referencing with other astrological software. The text report export provides a plain-text summary of planetary positions and aspect data.