Synastry chart calculator: how well do you match?

Synastry lays one birth chart over another and reads the angles between them, called aspects. A trine or a sextile tends to feel supportive, while a square or an opposition tends to feel livelier. It is an old and simple way of describing how two skies interact.

NovaOracles computes both charts from real astronomy, the same engine behind our birth chart tool, so the aspects are accurate to the arcminute. Nothing here is guessed, and nothing is sent anywhere: both charts are worked out in your browser.

Enter two sets of birth details and the calculator places every planet in both charts, then measures the angle each planet in one chart makes to each planet in the other. Angles close to a recognized aspect count; the rest are set aside. An exact time sharpens each Moon and the chart angles, so with both birth times the reading is at its most precise.

Because it works from the real positions rather than Sun signs alone, two people who share a Sun sign can still get very different readings. That is the point of it: zodiac compatibility lives in the whole chart, not one placement.

Astrologers read the supportive aspects, the trine and the sextile, as the places where two charts flow: shared ease, natural understanding, things that click without effort. The harder aspects, the square and the opposition, mark where the two rub, and that friction is often where the interest and the growth are.

A conjunction, where two planets sit on the same degree, amplifies whatever those planets stand for. Astrologers treat the mix as a description of the weather between two people, not a verdict on whether they belong together.

Sun conjunct Moon in synastry means one person's Sun sits within a few degrees of the other person's Moon. A conjunction blends and intensifies two planets, and this one joins the part of one person that wants to be seen with the part of the other that feels and needs. Tradition reads it as one of the warmest contacts two charts can make: the Sun person lights up the Moon person's inner life, and the Moon person helps the Sun person feel at home.

Venus conjunct Mars between two charts joins the way one person loves with the way the other pursues and pushes, and tradition reads it as strong attraction, with sparks that need some care. This calculator counts a conjunction up to 8 degrees apart and weights the Sun, the Moon, Venus and Mars most heavily in its harmony index, so either contact moves the result more than the same angle between other planets.

Sun signs alone sort millions of people into twelve boxes. This calculator looks further, at where each person's Moon, Venus and Mars fall and at how those points speak to the other chart.

That is why this tool asks for full birth details rather than two star signs. The Sun says something about the core, but the Moon carries how you feel, Venus how you love, and Mars how you clash and make up, and those are where a connection is really tested.

The most useful way to take a synastry reading is as a description of the space between two people, not a score to pass or fail. Every pairing has its easy aspects and its friction, and that friction is often what keeps a connection alive rather than what dooms it.

Take the lines that ring true, set aside the ones that do not, and use the reading to start a conversation rather than to settle one. Charts describe the weather, and the two of you still choose what to do in it.

The harmony index is a plain summary of the aspect set, weighted so the Sun, Moon, Venus and Mars count for more. Fifty is a balanced, mixed connection; higher leans easy, lower leans spicy. Neither is better than the other.

Treat it as entertainment and reflection. A low score is not a warning and a high score is not a promise: the most compatible pairs still have to do the work, and the spikiest can thrive on it. Read the number as a starting point for a conversation.

You need a birth date and place for each person; the birth times are optional but sharpen the Moon and the chart angles. The calculation runs in your browser and the tool is free. The Venus sign calculator and the Mars sign calculator show the two planets that matter most in love.

Compatibility and synastry explained walks through the method, the compatibility guide gathers the basics, and the birth chart calculator shows each chart on its own.