Free Synastry Chart Calculator

What Is a Synastry Chart?

A synastry chart is a relationship astrology chart that compares two natal charts side by side. Instead of describing one person, it shows how your planets talk to each other—where attraction sparks, where you soothe each other, and where friction asks for growth.

On Astro Seek, your free synastry chart highlights major aspects between both charts, then pairs the map with clear interpretation so you are not left staring at glyphs. Use it for romance, friendship, family, or business partnership compatibility.

• Birth chart — your personal cosmic blueprint (free birth chart).
• Synastry chart — how two blueprints interact (this page).
• Composite chart — the relationship as one midpoint chart (composite tool).

Synastry Charts Compare Two People — Composite Charts Describe the Relationship Itself

A synastry chart keeps both people intact. It asks how your Sun lands on their Moon, how your Venus meets their Mars, and which contacts repeat. You are still two charts.

A composite chart folds the two into one midpoint chart. That chart is not “you” and not “them.” It describes the relationship as its own thing: the tone you create when you are together, the job the bond seems to have.

Use synastry when the question is chemistry and friction between two people. Use the composite chart when the question is what the relationship is. The calculator above runs without an account. Deep Report and Vivian Q&A stay separate.

Synastry Compatibility Calculator

A synastry compatibility calculator is not a single “percent match” score. Real compatibility is a pattern: Sun–Moon harmony for feeling understood, Venus–Mars for attraction, Mercury links for how you argue and repair, Saturn contacts for longevity.

Astro Seek’s calculator surfaces those patterns so you can weigh chemistry and challenge honestly—better than a vague love score. Run the form above, then read the aspect guide below to decode what you see.

Relationship Astrology Chart: What You Can Discover

Exploring family overlays? Use the parent–child chart. Timing a relationship chapter? Check transit charts.

Planetary Aspects in Synastry

Aspects show how two people’s energies meet. Soft aspects ease the bond; hard aspects add heat and growth.

How to Read a Synastry Chart in 4 Steps

House overlays only count when both birth times are real. If one time is a guess, stay with planet-to-planet aspects and skip “their Venus is in your 7th house.”

• Synastry vs. composite — when the midpoint chart is the better next step.
• Birth chart without a birth time — what stays usable in a synastry chart.
• Composite chart calculator — the relationship as one chart.

Example: Sun in Leo With Moon in Pisces

Take one person’s Sun in Leo and the other’s Moon in Pisces. Leo wants the bond to be visible: warmth, praise, a shared stage. Pisces feels first and protects the feeling by softening edges. Being admired can land as being seen. It can also land as being put under a light the Moon did not ask for.

By sign, Leo and Pisces sit about 150° apart. That is a quincunx, not a square, a trine, or an opposition. There is no clean “you fight” and no clean “you flow.” The adjustment is awkward: the Leo person offers a performance of love, the Pisces Moon wanted a private mercy. Neither is wrong. The miss is the method.

Scale matters. This is the climate of the relationship, not a bad week. It shows up on ordinary days — how a compliment is received, how solitude is read as rejection, how one person wants a story and the other wants quiet. The useful move is specific. The Leo Sun asks what felt like too much exposure. The Pisces Moon says the need out loud instead of disappearing.

Example: Venus–Mars Square Between Two Fixed Signs

Now a faster contact: Venus in Taurus square Mars in Leo. Both signs are fixed. Taurus Venus wants steady touch, familiar pleasure, and a pace that does not restart the courtship every Friday. Leo Mars pursues in a way that wants to be noticed — bold, proud, a little theatrical. The square is about 90°. The desire is mutual and the style collides.

Fixed signs do not change direction to be polite. The same argument returns: one person experiences pursuit as pressure, the other experiences steadiness as a closed door. That heat is often obvious in the first month and in fights. It is not the structure of a twenty-year bond. Sun–Moon is the weather you live in. A Venus–Mars square is the match you notice first. Read it as chemistry with a repeating instruction, not as proof the relationship fails.

What helps is a change of method, not a change of goal. Taurus still wants reliability. Leo still wants a response that can be felt. Agreeing on one concrete gesture — a plan that stays, or a pursuit that waits to be met — does more than debating who is “too much.”

Synastry by Planet

Read the planet that is doing the contacting before you mix every glyph into one score.

• Sun synastry — identity meeting identity. Who feels recognized, and who feels crowded.
• Moon synastry — comfort, habit, and the private mood of the house you share.
• Venus synastry — affection, taste, and what counts as being loved.
• Mars synastry — pursuit, anger, and sexual pace. The planet that starts things.
• Mercury synastry — how a disagreement gets repaired. If this is hard, love still needs a translator.
• Saturn synastry — commitment, time, and the contact that either builds a spine or feels like a critic.
• Jupiter synastry — where the other person makes life feel larger. Generosity, or a promise that overreaches.

Synastry by Aspect

• Sun–Moon — does each person feel understood. Start here. Both directions.
• Venus–Mars — attraction style against desire style. Loud early. Not the whole chart.
• Moon–Moon — the daily emotional rhythm after the spark has a name.
• Saturn contacts — what holds the bond, or what feels heavy until it becomes structure.
• House overlays — where their planet falls in your houses. Only when both birth times are documented. If a time is guessed, stay with the planet pairs above and the birth-time guide.

Synastry by Purpose

Frequently Asked Questions About Synastry Charts