To calculate synastry and check compatibility with someone else’s chart, NatalChart.AI compares two fully calculated birth charts — every inter-chart aspect plus house placements overlaid in both directions. It works for friendship, family and collaboration as much as for romance, not only couples, and it returns a pattern map of where two charts meet with ease or friction — never a yes/no verdict. The flow is simple: create your own free natal chart, invite a friend or enter their birth data, then compare the two.
What real synastry looks at
- Inter-chart aspects — one person’s planet aspecting the other’s, with exact orb. Sun-Moon conjunctions, Venus-Mars trines, Saturn-Sun squares, everything.
- House overlays, both directions — which of their houses your planets fall into, and vice versa. Same two charts, two different overlay maps.
- Angle interactions — conjunctions and aspects to the Ascendant, Midheaven, Vertex.
- Composite-style themes — the AI surfaces where the two charts together create a recurring pattern (e.g. repeated Venus-Saturn aspects often surface as a pull between intimacy and structure).
What you actually see
- A list of inter-chart aspects, each with planet pair, aspect type, and exact orb.
- Two overlay diagrams: your planets in their houses, theirs in yours.
- A chart-grounded AI summary that names actual aspects (e.g. “your Venus opposes their Saturn at 1.2° orb, in their 7th house”) instead of generic compatibility text.
- Areas of natural ease, areas of friction, and how each person brings something out in the other — framed as patterns, not predictions.
Why chart-grounded matters here
Generic AI compatibility tools usually run a sun-sign lookup or improvise plausible text from two names. Both are nearly useless: dozens of pairs of charts share the same two suns and play out completely differently in real life.
Real synastry depends on calculation. The Venus-Mars aspect, the Saturn-Moon contact, whose Pluto sits on whose 8th house cusp — these are ephemeris-grade facts that change the whole relationship picture. NatalChart.AI calculates them with Swiss Ephemeris and locks the AI to those calculations through Chart-Locked AI Reading.
Frequently asked questions
What is synastry?
Synastry is the astrological practice of comparing two natal charts to study the relationship between them. It looks at inter-chart aspects (e.g. one person's Venus aspecting the other's Mars) and house overlays (which of your partner's houses your planets land in, and vice versa).
How is this different from sun-sign matching?
Sun-sign matching only compares two zodiac signs out of dozens of factors. Real synastry compares every planet, angle and house in both charts, with their exact aspects and orbs. The picture is far richer and far more specific to the two actual people.
What does NatalChart.AI's synastry actually compute?
Inter-chart aspects between every pair of bodies (one chart's planet vs the other chart's planet), with the canonical aspect angles and orbs. House overlays from both directions — your planets in their houses, and theirs in yours. Both charts are calculated independently with Swiss Ephemeris before any comparison runs.
Can the AI tell me if we're compatible?
It can describe how the two charts interact — where there's natural ease, where there's friction, what each person tends to bring out in the other. It will not predict whether the relationship will last, and it won't reduce two real people to a yes/no compatibility score.
Do we both need exact birth times?
Inter-chart aspects work even without exact times for both people, but house overlays and angles (Ascendant, Midheaven) need exact times to be meaningful. The reading marks which factors are time-sensitive, and exact times sharpen the interpretation considerably.
Can I calculate synastry with a friend's chart?
Yes. Synastry is not only for romance — it works just as well for friendship, family and collaboration. Any two people with birth data can be compared, and the reading describes how the two charts meet rather than assuming a romantic frame.
Do both people need exact birth times?
An exact birth time sharpens the Moon, Ascendant, houses and the house overlays between the two charts. Without it, planet-to-planet aspects between the two charts still work and remain meaningful, but the house overlays are less certain. The reading flags which factors depend on birth time.
What is the difference between synastry and a composite chart?
Synastry compares person A's chart directly to person B's — every inter-chart aspect and both directions of house overlay. A composite chart instead builds a single midpoint 'relationship chart' from both charts and reads it as one entity. NatalChart.AI currently supports synastry (two-chart comparison); it does not compute a composite chart.
Can AI tell whether we are compatible?
It maps strengths and friction across life spheres using the actual inter-chart aspects between the two charts. It does not issue a compatibility verdict, and it does not offer any soulmate guarantee — the point is reflective insight into how two charts meet, not a score or a fate.