Free tool
Compare two charts, not two scores.
Enter both birth records to calculate chart-to-chart aspects. Astrarium shows the actual contacts and orbs instead of compressing a relationship into a percentage.
Synastry cannot establish consent, character, compatibility in practice, safety, or whether a relationship should continue.
What synastry compares
Synastry places the planets of one chart in angular relationship to the planets of another. Sun–Moon contacts can describe identity and regulation; Mercury contacts describe communication; Venus and Mars describe attraction and pursuit; Saturn often describes commitment, pressure, time, or responsibility.
Why there is no universal compatibility score
The same aspect can be lived skillfully or destructively depending on maturity, context, power, communication, and choice. A single number hides those conditions and creates false precision. Astrarium keeps the aspect list inspectable.