Zodiac Compatibility Checker

How a birth date becomes a sign

The tropical zodiac is a measuring tape on the ecliptic, the Sun's apparent path. It starts at the March equinox, 0 degrees of Aries, and divides the circle into twelve signs of 30 degrees. A planet at 83 degrees is 23 degrees of Gemini. A planet at 190 degrees is 10 degrees of Libra. The sign is the floor of that longitude. The degree inside the sign is what is left over, truncated, so 23.8 is still reported as 23. Truncation keeps a body that is almost in the next sign from being announced as already there.

The longitudes come from the same astronomy library this site uses for the sign dates. The Libra page's 2026 equinox, 00:05 UTC on September 23, is that library. So is the Human Design chart, which reads Sun, Moon, Venus, and Mars at a birth instant. The checker calls those same positions. Nothing on this page is a hand-assigned match between sign names.

A date with no time is read as a Universal Time day, from 00:00 to 23:59. If a body is in one sign at both ends of that day, the sign is reported from noon Universal Time, and the degree is that noon's degree. If the sign at the start and the sign at the end differ, the checker names both and stops. It does not pick the one that makes the couple look smoother.

A worked pair, with the Moon left open

Take June 15, 1991, and October 3, 1988, both as dates with no clock. At noon Universal Time the first Sun is 23 degrees of Gemini and the second is 10 degrees of Libra. Venus on the first date is 9 degrees of Leo. Mars is 11 degrees of Leo. On the second date the Moon is 19 degrees of Cancer, Venus is 28 degrees of Leo, and Mars is 3 degrees of Aries. Those signs hold from the start of the Universal Time day to the end, so a clock is not required for them.

The Moon on June 15, 1991 does not hold. It begins the Universal Time day in Cancer and ends it in Leo. A love reading that quietly picked one of those Moons would be choosing a personality for someone. The checker leaves that Moon blank and asks for a time. That is the whole point of the optional clock.

The two Suns, which are firm, read like this. Sun and Sun stand 107 degrees apart. The nearest major angle is a trine, 13 degrees off 120, outside the 6 degree orb. By sign this pair is a trine by sign. Gemini and Libra share air. Four signs apart is the trine family, the old name for signs that share an element. The degrees themselves, 107, sit wide of 120, so the checker does not call the Suns a trine. The family and the degree are both true, and they are not the same claim. A page that collapsed them into "trine, therefore easy" would be throwing away the part you can measure.

Venus of the first chart to Mars of the second is a tighter story. Venus and Mars stand 126 degrees apart. That is inside the 6 degree orb of a trine. Both are fire, Leo and Aries, and the degrees agree with the sign family closely enough to name the angle. The other way, Mars of the first to Venus of the second, is the same sign and a wide gap. Mars and Venus stand 17 degrees apart. The nearest major angle is a conjunction, 17 degrees off 0, outside the 8 degree orb. By sign this pair is the same sign. Same sign, not a conjunction. Say both, or you have talked yourself into a closeness the sky did not give you.

The sun-sign sketch for this pair lives at Gemini and Libra. It is the general chapter on two air signs. It does not know that the 1991 Moon changed sign, and it does not know the 126 degree trine. Use the sketch for the signs. Use the checker for the two birthdays in front of you.

What a time and a city add

A birth time without a city is read as Universal Time. That is honest, and it is often the wrong zone. 8 p.m. in New York in July is midnight Universal Time, already the next date. The evening of a birthday in the Americas can belong to the next Universal Time day. If you are near a sign change, that is the difference between two readings. Add the city.

The city list is the one the Human Design chart uses, with a latitude, a longitude, and a time zone. The checker turns the clock you typed into Universal Time with that zone, including the daylight-time rules the zone carries. It then reads the sky at that instant. Every body on the form is settled to the minute. There is no start-of-day and end-of-day split, because the minute has been named.

The rising sign needs the place as well as the minute. It is the degree of the ecliptic on the eastern horizon. The library gives Greenwich sidereal time. The city's longitude shifts that to local sidereal time, and the latitude plus the obliquity of the ecliptic turn the horizon into a zodiac degree. This page allows that arithmetic between 66 degrees south and 66 degrees north. Closer to a pole, the horizon and the ecliptic meet in ways this form will not pretend to settle, and the rising line is left blank on purpose.

Rising is how a person comes into a room. It is not a second Sun, and it is not a moral quality. Two rising signs in a square can still share a kitchen. The angle tells you the weather at the door. The people still decide whether to come in.

Elements and modes, once the signs are known

Fire is Aries, Leo, and Sagittarius. Earth is Taurus, Virgo, and Capricorn. Air is Gemini, Libra, and Aquarius. Water is Cancer, Scorpio, and Pisces. In a couple, a shared element is a shared pace. Two air signs answer each other in talk. Two water signs answer each other in memory and loyalty. Fire with fire starts things and can scorch the same afternoon. Earth with earth builds, and can also stall in the same habit.

Different elements are not a failing grade. Fire and air feed each other when someone tends the draft. Earth and water hold a garden when someone agrees what "enough" means. Fire and water, or air and earth, have to translate. The translation is the work. It is also where a couple gets specific: a Leo Sun and a Scorpio Moon in the same person is already that translation, before a second person arrives.

Mode is the other old sort. Cardinal signs start a season: Aries, Cancer, Libra, Capricorn. Fixed signs hold: Taurus, Leo, Scorpio, Aquarius. Mutable signs adapt: Gemini, Virgo, Sagittarius, Pisces. Two cardinal people both reach for the plan. Two fixed people both keep the plan they already like. Two mutable people can renegotiate until the errand is missed. A cardinal with a fixed sign feels the classic rub, which is also why squares cluster there. The mode does not rank anyone. It tells you which argument you are likely to repeat.

The five angles, and the orbs this page uses

An aspect is a separation along the ecliptic, folded so it is never more than 180 degrees. Five of them are old enough, and plain enough, to name. The orb is how far from the exact angle this checker will still use the name. Outside the orb, the name is withheld and the degree is left standing on its own.

The orbs are wider for the conjunction and the opposition because those angles are the ones a couple feels across a few degrees of slop, and tighter for the sextile because 60 degrees is easy to counterfeit. A separation of 70 degrees is not a sextile on this page. It is 70 degrees. The sign family can still be named beside it, the way Gemini and Libra are a trine by sign while their Suns at 107 degrees are not a trine by degree. Keeping both sentences is the method. Collapsing them is how percentages get invented.

The checker reports six pairs, not every body to every other body. Sun to Sun is the style of the two lives. Moon to Moon is the daily need, when both Moons are known. Venus of one to Mars of the other, both directions, is the old question of what one enjoys and how the other pursues. Each Moon to the other Sun asks whether the daily need recognizes the other person's Sun. That is enough for a first honest look. A full synastry, with houses and the rest of the sky, is the birth chart reading.

How to read what comes back

Start with whatever was left blank. A blank Moon is information. It means the date was not enough, and any story you tell about feelings that day is a guess. Fill in the time before you build a theory of the person.

Then read the Sun line aloud in ordinary words. "We are both air, and the Suns are 107 degrees apart, wide of a trine." If you cannot say it without a special voice, you have not finished. The degree is allowed to disappoint the sign family. That disappointment is often the most useful line on the page, because it stops you from quoting a meme about your signs.

Venus is what a person warms to: the tone of affection, the setting, the beauty that counts for them. Mars is how a person goes after what they want, including how they argue and how they want to be met. Venus trine Mars, inside the orb, is a style that recognizes itself. It is not a guarantee of fidelity, and it is not a substitute for a conversation about what either of you actually asked for. Mars and Venus in the same sign but 17 degrees apart share a dialect and miss the conjunction. You can enjoy the same room and still be out of step inside it.

If both rising signs are present, read them last. They describe the door, not the household. A couple can have a severe rising square and a gentle Moon-Moon. Lead with the door and you will mis-tell the house. Lead with the Suns alone and you will miss the door. The order on the result is the order to talk about them.

Then do something the angles cannot do. Put a plan on a day. A Thursday call. A question you have been orbiting. The love tarot reading is the instrument for "what do I say," once the sky has told you which weather you are saying it in. The sky is the climate. The sentence is still yours.

Why this is not a score

The compatibility hub already refuses a percentage, and this tool is built to agree with that refusal. A score would need a weight for each angle, a weight for each blank, and a story about why a trine outranks a square in a life that may need the square. Those weights would be mine, dressed up as the sky. The sky gave degrees. The degrees are on the page. You can see the orb. You can see when a name was withheld. That is the whole derivation. There is no hidden total behind it.

The 78 pair pages stay up for anyone who arrives with two sign names and no birth times. Each is one unordered pair, Aries with Libra once, not also Libra with Aries. Search engines are asked not to file those sketches one by one. The hub and this checker are the pages meant to be found. When the checker knows both Suns, it links the sketch. Following that link does not make the sketch a second copy of your chart, and it does not put the sketch into the index. It is a chapter title. You already have the paragraph.

What no angle on this page can see: a rising sign without a city, a house, a Saturn return, a family, a debt, a child, a lie, a good Tuesday. Two charts can be elegant and the week can still be unkind for reasons that have street addresses. Foretold is a mirror for reflection. It is not a promise, and it is not advice about whether to stay.

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