Love Astrology
A synastry reading compares two complete birth charts, point by point, instead of comparing sun signs. Give the engine a birth date, time, and place for each of you — an exact time is what unlocks house overlays and precise Moon placements, but the reading still runs on the rest of the chart without one — and it computes both charts independently with the same engine used for individual consultations, then overlays them and reports where they interlock: which planets sit in conjunction, opposition, square, trine, or sextile between the two charts, and which house in the other person's chart each planet falls into.
What you get back is a compatibility reading built from that overlay, with the placements it rests on named alongside it — computed from two real birth times, not looked up by sign pairing.
Two charts in, one overlay out
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Add both birth charts
Enter birth date, time, and place for you and your partner. Place is always needed for the calculation itself; an exact time is what turns on house overlays and precise Moon placements — without it, the reading still runs on the rest of the chart.
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Both charts are computed
Each chart is calculated independently with the Swiss Ephemeris — the Sun through Pluto, the angles, and the houses — using the Placidus house system.
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The overlay is read
The two charts are compared point by point for aspects, and each person's planets are placed into the other's houses. The reading is written from that computed overlay and names the placements it rests on.
Aspects and house overlays, in plain language
An aspect is the angular distance between two planets. When a planet in your chart sits close to a fixed angle from a planet in your partner's chart, the two are "in aspect." Five angles are checked — conjunction (0°), opposition (180°), square (90°), trine (120°), and sextile (60°) — each allowed a small margin, an orb, so a near-exact angle still counts: 6° for conjunction and opposition, 5° for square and trine, 3° for sextile. Pairings where both points are slow outer planets — Uranus, Neptune, and Pluto to one another — are skipped: those sit at the same angle for everyone born in the same years, so they describe a generation rather than this pair. If a pair of planets is close enough to match more than one angle, the tightest match is the one reported.
A house overlay is what happens when one partner's planet falls inside a specific house of the other partner's chart — their Venus in your seventh house, for instance, the house synastry associates with partnership. The reading reports overlays in both directions, your planets into their houses and theirs into yours, but each direction depends on that target chart's houses being usable, which needs a known, exact birth time for that person; if one partner's birth time is approximate or unknown, overlays into that person's houses are left out, though the other direction can still run.
Ephemeris: Swiss Ephemeris, computed from its built-in Moshier model (this deployment ships no separate ephemeris data files). House system: Placidus. Points compared: the ten bodies from Sun through Pluto, except that a pairing of two slow outer planets — Uranus, Neptune, or Pluto to one another — is skipped as generational. Aspect orbs: conjunction 6°, opposition 6°, square 5°, trine 5°, sextile 3°.
Why exact birth time matters
Birth time sets the houses — the twelve life areas a chart is divided into — through the Placidus house system, so house overlays are only as good as the time behind them. It also moves the Moon, which shifts roughly 12–13° a day, enough to change its sign or house within a few hours. Without a known birth time we still compute a synastry reading, but house overlays for that chart are left out. Moon placements are still named in the reading like any other fact; what changes is that the reading adds a general note that Moon-related conclusions depend on birth-time accuracy, rather than flagging each Moon-based line on its own.
If it wasn't computed, it isn't in your reading
Whether a topic like communication, conflict, or boundaries appears in your reading at all depends on whether your two charts actually produced evidence for it — a section only exists when there is real computed evidence behind it. Each section that appears names the specific aspects or house overlays that qualified it, drawn only from what the engine computed for your pair, and the system refuses to publish a section that names a placement it never computed. Which facts get named there is computed; the sentence explaining what that kind of combination tends to mean is fixed wording for that section type, not rewritten placement by placement. The complete list of computed evidence behind a reading is not rendered anywhere in the product today — what's named inline in an actual reading is the strongest few placements per topic, not the full ledger.
Read it as a description, not a decision
A synastry reading tells you where your two charts line up and where they pull against each other. What you do with that stays yours. Naming what a contact means for you and your partner is interpretive work, not measurement, and it is not predictive: nothing here forecasts what your future together holds, and nothing here is a verdict on whether two people should be together.
Read the full computation methodologyBrowse the synastry library: worked examples by pairSee a synastry reading for your two charts
Compatibility readings run on the Yearly plan, with a one-time option shown when it is available. Compare access and pricing on the plans page.
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