Free tool
Synastry Chart Calculator
In plain English Synastry shows which parts of two people line up, clash or click.
A synastry chart compares two birth charts by laying one person's planets over the other's and listing the aspects between them. Enter both birth dates, times and cities above to get the full aspect table, a plain meaning for each aspect and the composite chart.
What a synastry chart shows
In plain Englishsynastry is a list of how two people’s charts touch each other.
Each person’s chart is a snapshot of the sky at birth. Synastry puts the two snapshots together and checks the angle between every planet in one chart and every planet in the other. A tight angle, called an aspect, links those two parts of the pair. Some aspects feel easy, some feel like friction, and most relationships have both. The compatibility calculator boils the same data into a score. This page keeps the full table.
How to read the aspect table
In plain Englishread the smallest orbs first, then look for the Sun, Moon, Venus and Mars rows.
The orb is the gap between the actual angle and the exact one, in degrees. A conjunction at 0.4 degrees is almost exact and hard to miss. A trine at 5 degrees is real but quiet. Rows involving the Moon say how safe you feel together, Venus how you show affection and Mars how you handle desire and conflict. Mercury rows are about conversation and Saturn rows about commitment, which can be steady or heavy depending on the aspect. Astrologers split on how much to read into any single row, so treat the table as a set of themes.
Free synastry chart interpretation
In plain Englishevery row has a plain line, and none of them is a verdict.
Each line names whose planet is whose and what the two parts of a person are about, then describes the aspect in everyday words. Tense aspects are not bad news: a square between two Mars signs often means two people who both like to win. Harmonious aspects are not a guarantee either, since a trine can mean comfort that nobody works on. Use the lines to start a conversation with the other person, not to settle one.
The composite chart
In plain Englishthe composite chart is the relationship treated as a third person.
For each pair of matching planets we take the midpoint, the point exactly halfway around the zodiac by the shorter route. The composite Sun is the midpoint of your two Suns and is read as what the relationship is for. The composite Moon is how the pair feels, Mercury how it talks, Venus how it loves and Mars how it acts and fights. We leave out houses and angles, because those need a shared birth location that two people rarely have. To compare two Sun signs only, use the compatibility calculator or the sign compatibility pages.
What to do next
In plain Englishcompare the signs, then check each person’s own chart.
Curious about one person at a time? The birth chart calculator shows every planet and house, and the moon sign calculator finds the most emotional part of each chart. Both are free.
Questions people ask
- What is a synastry chart?
- A synastry chart compares two natal charts. Astrologers lay one person's planets over the other's and note every aspect between them, such as one person's Venus sitting trine the other's Mars. The table above lists those aspects for the two charts you enter.
- How do I use the synastry chart calculator?
- Enter a birth date, time and city for each person, then press the button. You get a table with each planet of person A, the aspect, the planet of person B and the orb, plus a one line meaning for each row and a composite chart below it.
- Is this synastry chart really free?
- Yes. The free synastry chart needs no account and no email, and the full aspect table appears on the page. We ask for an email only after the result, and only if you want your chart saved.
- How do I read a synastry chart interpretation for free?
- Start with the tightest aspects, the ones with the smallest orb, because they are felt most. Then look at where Sun, Moon, Venus and Mars of one person touch the other, since those four carry most of the chemistry and comfort. Each row above has a plain line to read.
- What is a composite chart?
- A composite chart treats the relationship as its own chart. It takes the midpoint between each pair of planets, so the composite Sun is halfway between your two Suns. Astrologers read it as the personality of the pair rather than of either person.
- What is a good orb in synastry?
- An orb is how far an aspect is from exact. Under 2 degrees is strong, 2 to 5 is clear, and wider than that is faint. Our calculator uses the standard synastry orbs and sorts the tightest aspects first.
- Do I need both birth times?
- No, but they help. Without a time the Moon can be off by up to 7 degrees, and the rising sign and houses are left out. The planets from Mercury outward are accurate with the date alone.
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