Checking compatibility by birth date is the most common request in astrology, and the most simplified one: usually it's comparing two zodiac signs against a "who's compatible with whom" table — Aries and Leo, good; Aries and Cancer, not so much. That table is based on something real — elements and sign qualities genuinely interact in particular ways — but it's the coarsest level of analysis that exists in compatibility astrology.
The real tool is called synastry — comparing not signs, but the full natal charts of two people: where every planet sits for one, where for the other, and how they relate to each other. One person's Sun can fall in the other's house of relationships; one person's Venus can form a harmonious aspect with the other's Mars. That's no longer "what are your signs" but exactly how your two personalities interlock — where you match, where you reinforce each other, and where you'll need to work things out.
A practical reading breaks down into several layers: an overall compatibility score, which aspects you match on most strongly, where the points of tension are and what's worth discussing early on, plus a separate look at elemental dynamics (if one of you is Fire and the other Water, it helps both of you understand where the difference in pace comes from), and a Chinese horoscope as one more short cross-section — for context, not instead of Western astrology.
By birth date alone — without time and place — the picture is always incomplete. Planet signs can still be compared, and that already gives something real. But each person's houses and exact ascendant — what shows which area of life the connection plays out in — are unavailable without both people's birth times. That's not hidden here: the reading honestly shows which part of the compatibility was calculated precisely and which wasn't.
Check your compatibility by birth date for free — add the time and place if you know them: the reading gets more precise, but you can start without them too.