Free tool
Synastry & Compatibility Calculator
Enter both birth dates, times, and places to see how two charts connect — the aspects between your planets, your composite chart, and where each person's planets land in the other's houses. Free, instant, and no account needed.
Enter both people's birth data
Partner A
:
Your birth details are used only to calculate this chart. They are not saved.
Partner B
:
Your birth details are used only to calculate this chart. They are not saved.
Still needed:Partner A: Birth Date · Birth Time · Birth CityPartner B: Birth Date · Birth Time · Birth City
Synastry calculator — questions
- Is the synastry calculator free?
- Yes — enter both sets of birth data and get the cross-aspects, composite chart, and house overlays instantly, with no account.
- Do I need both birth times?
- The cross-aspects and the composite chart's planet placements work from the dates and places alone - except where the Moon is involved: without a birth time it can sit anywhere along about twelve degrees, so its aspects can change once the missing time is added. The houses, Ascendant, Midheaven, and house overlays need both exact birth times.
- What is a composite chart?
- A composite chart is a single chart built from the midpoints between two people's planets. It represents the relationship itself as one entity, not the two people interacting.
- What is synastry?
- Synastry compares two birth charts by measuring the angles — the aspects — between one person's planets and the other's, where two charts connect, reinforce, and pull on each other.
- Why does another site rate the same two charts differently?
- Because compatibility is not a measurement. Sites differ in which aspects they count, how wide their orbs are, which house system frames the overlays, and whether they score at all — a number out of a hundred is a convention stacked on conventions. The positions themselves agree to the arcminute between any two serious calculators; the reading of them is where the disagreement lives.
The conventions this chart uses
None of these are facts of the sky. Each is a choice astrologers disagree on, so we list ours — a difference from another site can then be traced to its rule instead of blamed on the stars.
- Tropical zodiac
- Signs are tropical, anchored to the March equinox, not to the constellations. Sidereal (Vedic) astrology counts from the stars instead, which currently shifts every position by about 24 degrees — the most common reason two sites disagree about a sign.
- Placidus houses
- Houses are Placidus, the most widely used modern system. Whole-sign or Koch redraw the boundaries: they move planets between houses, never between signs. Beyond the polar circles Placidus is undefined, and we then show the chart without houses rather than guess.
- Mean lunar nodes
- The lunar nodes are mean (averaged). The "true" node oscillates around the mean by up to about two degrees — measured, at most 1°59' across two centuries.
- Mean Lilith
- Black Moon Lilith is the mean lunar apogee. The "true" (osculating) variant can sit up to about thirty degrees away — often a different sign, and the single biggest source of Lilith disagreements.
- Aspect orbs
- Natal orbs: conjunction and opposition 8°, square and trine 7°, sextile 5°, quincunx 3°. Toward the Ascendant and Midheaven the orbs tighten, and the quincunx is not counted there at all. A site with wider orbs lists more aspects, not different planets.
- Sect
- The Part of Fortune follows sect: a day birth (Sun above the horizon) uses Ascendant + Moon − Sun, a night birth the reverse. For night births, calculators that apply the day formula to everyone place it in a different sign roughly nine times out of ten.