Free Astrology Calculator

Birth Chart Compatibility Calculator (Synastry)

Your birth chart reveals the unique pattern of the sky at the moment you were born. When two charts are compared, astrology explores how these patterns interact.

Birth chart compatibility, also known as synastry, shows where two people naturally support, challenge, and inspire one another. Our calculator also provides a birth chart compatibility percentage, offering a simple way to visualize how strongly two charts resonate.

Enter the birth details of both individuals below. Our calculations use precise astronomical NASA data for accuracy.

Birth Chart Compatibility Calculator
PERSON A
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PERSON B
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Natal Chart

Natal Chart

Input details

Synastry Aspects

PLANETS AND POSITIONS GUIDE
SUN ☉ Your core identity, ego, and life purpose. It symbolizes your individuality and the way you express yourself. JUPITER ♃ Expansion, abundance, and growth. It signifies luck, optimism, and opportunities for personal and spiritual development.
MOON ☽ Governs your emotions, intuition, and instincts. It reflects your inner emotional world, moods, and subconscious patterns. SATURN ♄ Governs responsibility, discipline, and structure. It reflects your limitations, challenges, and the need for self-control.
MERCURY ☿ Communication and intellect. It influences how you think, process information, and express yourself verbally. URANUS ♅ Change and innovation. It represents individuality, originality, and unconventional thinking.
VENUS ♀ The planet of love and beauty. It governs relationships, romance, aesthetics, and your values related to pleasure and harmony. NEPTUNE ♆ The planet of dreams, intuition, and spirituality. It influences creativity, mysticism, and the ethereal realms.
MARS ♂ Energy, action, desire, and assertiveness. It guides your drive, motivation, and how you go after what you want. PLUTO ♇ The planet of transformation, power, and regeneration. It signifies deep personal changes, rebirth, and the uncovering of hidden truths.
NORTH NODE ☊ Represents one's life purpose or karmic direction, pointing towards growth, fulfillment, and personal evolution. CHIRON ⚷ Chiron represents our deepest wounds and the potential for healing and personal growth.
SOUTH NODE ☋ Represents skills and traits, as well as comfort zones we are encouraged to move away from for growth. MC MC Midheaven (MC) represents one's career path, public image, and aspirations, reflecting the potential for achievement and status in society.
RISING ⊕ Rising Sign (Ascendant) represents your self-image, outward personality, and the initial impression you make on others. IC IC The Imum Coeli (IC) represents one's roots, home life, private self, and foundation, reflecting the deepest part of the individual's inner world.
ASPECTS GUIDE
TRINE △ Harmonious and beneficial connection between two planets, indicating ease and natural talent in the areas they influence. SEXTILE ⚹ Opportunities and productive interactions between two planets, facilitating growth and cooperation in their influenced areas.
SQUARE □ Tension and challenge between two planets, prompting growth through overcoming obstacles in their influenced areas. OPPOSITION ☍ A challenging but potentially harmonizing relationship between two planets, indicating areas of life where balance and integration are needed.
CONJUNCTION ☌ Planets in the same sign, blending their energies and intensifying their combined influence.
Synastry Calculator FAQs

Birth Chart Compatibility Explained

Birth chart compatibility in astrology, also called synastry, is the comparison of two natal charts to understand how the two people interact, connect, and influence each other.

Rather than looking only at Sun signs, synastry examines the positions of the planets in both charts and the angles ( also called aspects)  they form with one another. When planets from one person’s chart create aspects with planets in another person’s chart, they reveal areas of harmony, attraction, tension, or growth within the relationship.

Astrological compatibility is therefore not about determining whether two people are simply “meant to be.” Instead, it reveals how two inner worlds meet, where they resonate naturally and where they may challenge each other to grow.

A birth chart compatibility percentage is calculated by analyzing the planetary aspects formed between two natal charts.

Some aspects are traditionally considered more harmonious, such as trines and sextiles, which often indicate ease and natural understanding. Others, such as squares and oppositions, can introduce tension or areas that require growth and adjustment. 

Our Birth Chart Compatibility Calculator examines these planetary connections and translates their overall quality into a percentage score, helping illustrate the balance between supportive and challenging dynamics in the relationship.

In astrology, a compatibility percentage is not a mathematical certainty. It is a symbolic way of summarizing the overall balance between harmonious and challenging planetary aspects in a synastry chart.

When two birth charts are compared, astrologers examine the connections formed between the planets of each person. Some aspects tend to flow more easily, suggesting natural understanding or attraction, while others may introduce tension, difference, or growth. A compatibility percentage translates the overall quality of these interactions into a simplified score.

In this sense, the percentage offers a general overview of the energetic dialogue between two charts, but the deeper meaning lies in how those planetary interactions unfold in real life.

Astrology can offer meaningful insight into relationship compatibility, but it does not predict relationships in a fixed or deterministic way.

Even the most harmonious synastry still require awareness, care, and mutual effort, while charts with challenging aspects can develop deep and meaningful bonds when both people learn how to work with those dynamics. Synastry therefore reveals the colors of the interaction, not its final outcome. It shows where understanding may come naturally and where growth, patience, or compromise may be needed.

In astrology, several planetary placements play an important role in relationship compatibility, but some connections tend to be particularly significant.

Among the most important are the two luminaries: the Sun and the Moon. When the Sun and Moon of two charts connect harmoniously, there is often a natural sense of recognition between identity and emotional expression.

Another key factor in synastry is the presence of precise planetary aspects. In astrology, the closer an aspect is, the stronger its influence tends to be. Connections within a tight orb , within about two degrees, can be particularly powerful because they indicate a very direct interaction between two planetary energies.

Sun sign compatibility can offer a general indication of how two personalities might interact, but it is not enough to fully understand a relationship.

Other placements often play an equally important (and sometimes even more revealing) role in compatibility. The Moon, for example, describes emotional needs and instinctive responses. When two Moons resonate, emotional understanding tends to come more naturally.

The Rising Sign (Ascendant) is also significant, as it reflects how a person approaches life and interacts with the world. Connections involving the Ascendant can influence how two people perceive and respond to each other in everyday interactions.

Planets such as Venus and Mars can reveal attraction and relational dynamics, while Mercury often shows how two people communicate and interpret each other’s thoughts.

For this reason, astrology looks at the entire dialogue between two birth charts, not just Sun signs. Synastry examines how all planetary placements interact, offering a more complete picture of the relationship dynamic.

Our Birth Chart Compatibility Calculator compares the full structure of two charts to highlight the planetary connections that shape how two people truly relate to one another.

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