Synastry: compatibility of two birth charts

By Emily Hart, professional astrologer · updated September 11, 2026

Synastry is the astrology of «us»: two birth charts laid over each other to see where the planets support, spark or grind. It's the professional answer to «are we compatible» — much deeper than Sun signs, because it compares the Moons (emotional needs), Venus and Mars (love and desire styles), and the aspects between all of them.

Start quick and honest: the checker below compares your two dates by Sun sign using our compatibility engine — a real first layer with a percentage and a full pair analysis. Below it, what the complete synastry adds.

Compatibility by date of birth: the quick check

First person's date of birthSecond person's date of birth

Full synastry calculator: two birth charts, real aspects

Now the professional layer, computed live: enter both dates (time and city too — the more exact, the better) and the calculator builds both charts on the Swiss Ephemeris, finds the actual aspects between your planets — Moon to Venus, Saturn to Sun — and reads them honestly.

What a full synastry reads that sun signs can't

The Moons: whether your emotional needs feed or starve each other — the factor behind «we love each other but keep hurting each other».

Venus and Mars: the love language and the desire language, and whether one chart's style lands for the other.

Aspects between charts: exact angles (his Saturn on her Sun, her Moon trine his Venus) — the concrete mechanics of attraction, friction and glue.

Houses activated: where the partner lands in YOUR life — the romance house, the career house, or the 12th-house fog.

Want the full two-chart reading?

A personal synastry reading computes both charts — Moons, Venus-Mars dynamics, exact aspects and houses — with honest windows of opportunity for the pair.

Order a synastry reading

Frequently asked questions

What is synastry in astrology?

The comparison of two birth charts: each person's planets are read against the other's — signs, houses and exact aspects. It maps where a pair supports each other and where the friction lives; percentages by Sun sign alone are just the first layer of it.

How accurate is a compatibility percentage?

As a comparison guide — useful; as a verdict — no. A Sun-sign percentage describes the two signs' general mechanics, not two specific people. Full synastry narrows it to your actual charts, and even then honest astrologers speak of tendencies, not guarantees.

Can two 'incompatible' signs have a great synastry?

Absolutely — it happens all the time. A tense Sun-sign pair can carry a beautiful Moon-Venus contact that outweighs everything. That's exactly why the full chart comparison exists: the Suns are two letters of a long alphabet.

What do I need for a full synastry reading?

Both birth dates, times and cities. Time matters: it sets the Moon's exact degree, the ascendants and the houses — the parts of synastry that answer «where does this person land in my life».