How zodiac compatibility works

Choose signs or birth details

Choose a first sign, a second sign, and a romance, friendship, or work lens. The month-and-day finder provides a conventional range. The exact lookup uses a birth year, local time and birthplace time zone to compare the birth moment with tropical Sun ingress times. When the time is unknown, it keeps both signs if the Sun changed on that local day.

Birth Moon signs and phases

The Moon sign calculator divides the Moon’s geocentric ecliptic longitude of date into twelve tropical 30° sectors, beginning with Aries at 0°. It covers 1900–2100 and uses the birthplace time zone’s historical clock rules. A skipped clock time is rejected; a repeated time needs a first or second occurrence. With no time entered, the calculator checks the whole local date and keeps both signs when an ingress occurs.

The birthday phase comparison uses the Moon’s geocentric Sun-relative longitude and illuminated fraction at each birth moment. A blank birth time uses local noon and is labelled in the result. Its north-up discs show illumination geometry, without libration or a site-specific horizon orientation.

Phase terminology follows the US Naval Observatory. Birth details are submitted privately and stay out of result links.

Find a birth Moon sign · Compare birthday phases

Tropical Sun sign boundaries

The five sign coordinates

Whole-sign distance

The shortest count between two positions on the twelve-sign wheel.

Nominal separation

Whole-sign distance multiplied by 30°, from 0° through 180°.

Element pairing

The exact combination formed by Fire, Earth, Air, or Water.

Modality pairing

The exact combination formed by cardinal, fixed, or mutable.

Polarity pairing

Whether the two signs use the same or different active and receptive classifications.

Traditional-ruler pairing

The classical planetary ruler attached to each sign.

Twelve signs create 78 unique unordered pairs, including 12 same-sign pairs. Swapping the order keeps the pair's whole-sign facts unchanged. The distance determines the whole-sign aspect family and nominal separation.

Element, modality, polarity, and traditional-ruler pairings come directly from the two sign records. Together with wheel distance, these are the fixed inputs shown on every pair guide.

The four element combinations

Western tropical sign readings group Fire with Air and Earth with Water; sharing an element names a familiar mode of expression. The table gives the symbolic grouping, alongside each sign’s separate communication and conflict themes.

For example, Aries Fire and Gemini Air pair initiative with an exchange of ideas. Taurus Earth and Cancer Water pair practical continuity with emotional care. A different grouping asks which style each person wants to understand, rather than assigning an outcome to the pair.

Cardinal, fixed and mutable combinations

Cardinal emphasizes beginning, fixed emphasizes maintaining, and mutable emphasizes adapting. Each mode has four signs. Read the complete table alongside the actual pair’s element and wheel geometry.

A cardinal/fixed pair can agree who starts a plan and how both sustain it. Two mutable signs can choose one dependable checkpoint before changing the rest. These are conversation themes within the named Sun-sign reading, alongside the complete sign comparison matrix.

Choose the right tool

• Use the comparator when you already know both conventional Sun signs.
• Use the month-and-day finder when one sign is still unknown.
• Use the birth-detail finder when a boundary date needs an exact Sun sign.
• Calculate a full relationship chart for planetary degrees, houses, Moon and rising placements.

Reading romance, friendship and work

Compare both people’s communication, emotional and conflict patterns alongside their sign coordinates. A shared element can describe familiar priorities; a different modality can describe a different pace.

The romance lens emphasizes affection and emotional rhythm; friendship emphasizes shared time and mutual care; work emphasizes roles and collaboration. Choose the context that fits the conversation you want to have.

Factor references

Sun signs and full synastry

• A full synastry reading also considers the Moon, Ascendant, planets, houses, and degree-based aspects.
• Exact Sun-sign boundaries near a cusp vary by year, time, and location. The month-and-day helper flags the dates around each conventional changeover.

Example: Taurus and Scorpio

Taurus and Scorpio

Calculated facts

Whole-sign relationship

Opposition · opposite signs

Nominal sign-position separation

180° between whole-sign positions; exact natal aspects use actual Sun positions

Elements

earth and water

Modalities

fixed and fixed

Read the Taurus and Scorpio pair guide