If you have ever wondered "are we compatible?" in astrology terms, the tool you are looking for is a synastry chart. It is the technique behind almost every serious piece of relationship astrology: instead of reading one person's birth chart, you lay two charts on top of each other and study how their planets connect. This guide explains what a synastry chart actually is, which aspects matter, and what "compatibility" honestly does — and does not — mean. You can build your own synastry chart as you read.
What a Synastry Chart Actually Is
A synastry chart (sometimes simply called a compatibility chart) takes two complete natal charts and overlays them. Each person keeps their own planets in their own signs and houses; the insight comes from the angles — the aspects — formed between one person's planets and the other's.
A synastry calculator does this mechanically:
- Calculate both birth charts from each person's date, exact time, and place.
- Overlay the two wheels so Person A's planets sit against Person B's, and vice versa.
- Measure the aspects between them — conjunctions, trines, squares, oppositions and sextiles connecting one chart's planets to the other's.
None of this is fortune-telling. It is geometry applied to two birth moments. What you do with the picture is the interesting part.
The Aspects That Matter Most
You do not need to read every planetary contact to understand a relationship. A handful of pairings carry most of the weight in relationship astrology:
- Sun–Moon — one person's Sun touching the other's Moon is one of the classic "we just get each other" signatures. It blends core identity (Sun) with emotional nature (Moon).
- Venus–Mars — the attraction axis. Venus is how you love and what you value; Mars is drive and desire. Strong Venus–Mars contacts often explain chemistry and physical spark.
- Moon–Moon — when two Moons connect, emotional rhythms line up. This is less about fireworks and more about whether you feel at home with each other day to day.
- Saturn contacts — Saturn to a personal planet can feel heavy or grounding. It is often the signature of commitment and longevity, not just difficulty.
A common misunderstanding: squares and oppositions are not "bad." They describe tension and friction — which can mean growth and magnetism just as easily as conflict. A relationship made only of easy trines can feel flat; one with some hard aspects often has more charge.
It also helps to notice which planets carry the contact. The same square feels very different between two Moons (emotional reactivity) than between Saturn and Venus (commitment that asks for patience). This is why a single "compatibility score" is misleading: a good synastry reading weighs the planets involved, the houses they fall into, and how tight the angles are — not just whether a contact exists.
What "Compatibility" Really Means
Here is the honest part. A compatibility chart does not score your love life out of 100, and no responsible reading produces a verdict of "yes" or "no." Synastry describes how two people's energies interact — where you flow, where you grind, what each person tends to bring out in the other.
Two charts with very "easy" contacts can still fail if the people ignore each other. Two charts full of friction can thrive when both partners do the work. Astrology maps the terrain; the people decide where they walk. Treat a synastry reading as a mirror for reflection, not a prediction of fate.
If you want a fuller walkthrough of the techniques, the astrology compatibility guide goes deeper, and the how to read a natal chart guide helps if you are still new to single-chart basics.
Synastry vs. Composite Charts
People often confuse the two, but they answer different questions:
Synastry
A synastry chart keeps both individuals intact and studies the contacts between them. It answers: "How do you two affect each other?" It is the better tool for understanding attraction, friction, and the lived feel of a relationship.
Composite
A composite chart mathematically merges two charts into a single new chart — the midpoints between each pair of planets — to represent "the relationship itself" as one entity. It answers: "What is the character of this partnership as a third thing?"
In practice, most readers start with synastry to feel the dynamic between two people, then look at the composite to understand the relationship's overall purpose and direction. A good synastry calculator focuses on the first; you can layer the second on top once the basics make sense.
Beyond Western Synastry
Western astrology is not the only system that reads relationships. If you are curious how Chinese astrology approaches the same question, the BaZi zodiac compatibility guide compares partners through the Four Pillars and Five Elements instead of planetary aspects. Different map, same honest principle: it describes tendencies, not destiny.
Build Your Synastry Chart Now
Ready to stop guessing whether are we compatible in astrology and actually see the contacts? Create your free synastry chart — enter both sets of birth details and read the Sun, Moon, Venus and Mars aspects between you in seconds. New to charts entirely? Start with a single free birth chart first, then come back and compare.