Synastry Chart Calculator

Compare two birth charts with a two-ring wheel, planetary placements and major cross-chart aspects. Keep astronomical separations separate from relationship interpretations.

Astronomical positions are calculated; astrology and numerology interpretations are symbolic, not scientifically validated assessments.

Chart A

DateTime unknown — use a labelled noon illustrationLocal timeReference cityIANA time zone (e.g. Europe/London)If the clock time occurred twiceLatitude (north positive)Longitude (east positive)

Reference cities use centre coordinates. Edit them for your actual birthplace. Historical offsets follow your browser’s time-zone database; check your record when clocks changed.

Chart B

DateTime unknown — use a labelled noon illustrationLocal timeReference cityIANA time zone (e.g. Europe/London)If the clock time occurred twiceLatitude (north positive)Longitude (east positive)

Reference cities use centre coordinates. Edit them for your actual birthplace. Historical offsets follow your browser’s time-zone database; check your record when clocks changed.

Calculations stay in your browser. We do not put birth details in URLs, storage or analytics. Results are not sent to a server.

Enter your details and choose Calculate. Examples are illustrative, not saved profiles.

How this calculation works

Each chart is resolved independently to UTC. The ten planets in chart A are compared with the ten planets in chart B for conjunction, sextile, square, trine and opposition within a six-degree orb.

Assumptions and limits

This is a planetary synastry comparison, not a composite chart or a relationship score. Unknown times produce noon illustrations; no rising or house overlay is inferred for them.

Questions about synastry chart

Does this tell me whether a relationship will last?

No. The aspect list is astronomical geometry with symbolic commentary; it cannot establish relationship quality or future outcomes.

Are both birth times required?

They improve accuracy, especially for the Moon. Unknown times are labelled as noon illustrations and should not be treated as exact natal placements.