NatalCalculator

Birth Chart Compatibility Calculator: Synastry Between Two Charts

Birth chart compatibility, measured instead of guessed at. Enter two sets of details and this free synastry calculator overlays the charts, listing every major aspect from one person’s ten planets to the other’s: the geometry all the talk is actually based on, never a score out of a hundred.

Compare two charts

Person A

Any date between 1800 and 2050.

Local clock time at the birthplace. Daylight saving is applied automatically.

Start typing a city name.

    Enter coordinates manually
    Person B

    Any date between 1800 and 2050.

    Local clock time at the birthplace. Daylight saving is applied automatically.

    Start typing a city name.

      Enter coordinates manually

      The two charts shown are a worked example. Replace either set of details and the comparison updates as you type.

      Person A

      A circular chart with the twelve signs around the rim, the twelve house cusps marked, and each planet drawn at its zodiacal degree.♈♉♊♋♌♍♎♏♐♑♒♓123456789101112☉12°31′☽5°54′☿15°00′♀11°35′♂24°38′♃20°09′♄22°45′ ℞♅7°23′ ℞♆13°13′ ℞♇15°06′ ℞

      Sun Cancer · Moon Sagittarius · Rising Libra

      Person B

      A circular chart with the twelve signs around the rim, the twelve house cusps marked, and each planet drawn at its zodiacal degree.♈♉♊♋♌♍♎♏♐♑♒♓123456789101112☉1°18′☽19°42′☿7°13′♀16°42′♂19°05′♃2°49′♄2°13′♅0°58′♆10°04′♇12°13′ ℞

      Sun Aries · Moon Taurus · Rising Gemini

      What this pairing shows

      The tightest contact between these two charts is Person A's Uranus sextile Person B's Mercury, exact to within 0°10′. Whatever these two planets represent between them is the loudest single thread running through this pairing - the one most likely to be recognisable early and to keep mattering.

      Person A's Moon trine Person B's Sun is present here too, within 4°36′. A Sun-Moon contact between two charts is one of the connections synastry treats as structurally significant - it links one person's core direction to the other's emotional footing, for better or worse depending on the angle involved.

      Across all 37 contacts found, trines and sextiles outnumber squares and oppositions, suggesting this pairing tends to flow with comparatively little friction - pleasant, though it is worth remembering that a chart with almost no hard contacts can also mean less is asked of either person, for the same reason a Grand Trine can go undeveloped.

      Inter-chart aspects

      Every major aspect from Person A's ten bodies to Person B's ten, tightest orb first.
      Person AAspectPerson BOrb
      Uranus SextileMercury0°10′
      Sun TrinePluto0°19′
      Jupiter SextileMoon0°26′
      Neptune SextilePluto1°00′
      Jupiter OppositionMars1°04′
      Moon SquareMercury1°19′
      Pluto OppositionVenus1°37′
      Mercury SextileVenus1°42′
      Sun OppositionNeptune2°27′
      Uranus ConjunctionNeptune2°41′
      Mercury TrinePluto2°48′
      Pluto ConjunctionPluto2°53′
      Saturn TrineMoon3°03′
      Neptune ConjunctionNeptune3°08′
      Jupiter SextileVenus3°26′
      Neptune TrineVenus3°30′
      Saturn ConjunctionMars3°40′
      Pluto SextileMars3°59′
      Mercury OppositionMars4°05′
      Sun SextileVenus4°11′
      Venus SquareMercury4°22′
      Uranus TrineJupiter4°35′
      Moon TrineSun4°36′
      Pluto OppositionMoon4°37′
      Mercury SextileMoon4°42′
      Uranus SextilePluto4°49′
      Mercury OppositionNeptune4°56′
      Uranus ConjunctionSaturn5°11′
      Sun TrineMercury5°18′
      Mars SquareMars5°33′
      Neptune ConjunctionMars5°52′
      Saturn TrineVenus6°03′
      Uranus SquareSun6°06′
      Mars TrineUranus6°19′
      Uranus ConjunctionUranus6°26′
      Neptune TrineMoon6°30′
      Sun OppositionMars6°34′

      What synastry measures - and does not

      Every one of Person A’s ten bodies is checked against every one of Person B’s ten, which is a genuinely different calculation from a single chart’s own aspect list: “A’s Sun square B’s Mars” and “B’s Sun square A’s Mars” are two separate, independent facts about the pairing, not the same fact counted twice, so this is a full ten-by-ten comparison rather than the triangular count a single chart uses on itself. What comes out is a list of contacts, not a conclusion. Read it the way you would read the aspects in your own chart: as raw material that plays out differently depending on everything else going on between two real people.

      How to read an inter-chart aspect

      Take “Person A’s Venus square Person B’s Mars” as a worked example of the shape these read in. Venus is what a person finds desirable and how they seek harmony; Mars is how a person pursues what they want and expresses friction. A square between the two means Person A’s taste and Person B’s drive rub against each other rather than aligning smoothly - which can register as real attraction precisely because it takes effort, or as recurring friction over pacing and approach, and very often as both at different points in the same relationship. The aspect names the contact; it does not settle which flavor will dominate.

      Composite charts: a related but different technique

      A composite chart is not what this page builds. Rather than comparing two charts side by side, a composite chart merges them - typically by taking the midpoint of each pair of corresponding planets - into a single new chart that is read as if it belonged to the relationship itself. It answers a different question ("what does this relationship look like as its own entity?") from the one synastry answers ("how do these two specific people's placements interact?"). See the glossary entry for a fuller definition.

      Frequently asked questions

      What does synastry actually measure?

      Synastry overlays two real charts and measures the aspects - the angles - between one person’s planets and the other’s. That is all it measures directly: a set of geometric relationships between two sets of placements. It does not measure whether two people are compatible in any single summarizable sense; it describes dynamics, some of which feel supportive and some of which feel like friction, and both kinds show up in relationships that work and relationships that do not.

      Does a hard aspect (square or opposition) mean incompatibility?

      No. A square or opposition between two charts means tension that has to be worked with, not a verdict against the relationship - plenty of long, close relationships run on exactly this kind of friction, often because it is what keeps both people engaged rather than complacent. A chart with only easy aspects (trines and sextiles) is not automatically the stronger pairing either: ease can mean nothing is being asked of either person.

      Is this a compatibility score out of 100?

      No, deliberately. A single score collapses dozens of distinct, sometimes contradictory dynamics into one number, which flatters the tool more than it informs the reader. This page shows the actual aspects found, tightest first, and a summary grounded in what was actually calculated - not a manufactured percentage.

      What is a composite chart, and is it the same as synastry?

      No - a composite chart is a different, related technique: rather than comparing two charts to each other, it mathematically merges them into one new chart (typically by taking the midpoint between each pair of corresponding planets) that is read as representing the relationship itself, as though it were a third entity. Synastry, what this page computes, keeps the two original charts separate and looks at the aspects between them. This calculator does not currently build a composite chart.

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