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Synastry calculator

This synastry calculator lists every aspect between two birth charts, and next to each one how many random pairs already have it. Its score is judged against 400 sampled pairs, which average 56.6.

What the calculator reads: synastry aspects, house overlays, zodiac compatibility, kundli matching, Mars Opposition Venus, Mars Square Pluto, Mars Conjunction Moon, Mars Square Moon, Pluto Square Venus and Lilith Opposition Venus.

Synastry Calculator: Two Charts, Scored Against a Baseline
First chart
Second chart

Computed across 400 sampled pairs

The “rare” aspects are not rare

Synastry content leans hard on the idea that certain contacts are special. Between two arbitrary birth dates the most frequent inter-chart aspect turns up about one time in five.

The eight most frequent aspects between two random birth dates, either way round
The eight most frequent aspects between two random birth dates, either way round Two people's planets are independent of each other, so the geometry sets the base rate: a square or trine with a 7° orb lands one way round in 7.78% of pairs and either way round in about 15%. The top eight sit a little above that because they are the top of about sixty such counts, and with 400 pairs each count can drift by ±3.6 points. Mars square MercuryMars square Mercury: 19.5%19.5%Mars trine MoonMars trine Moon: 19%19%Mars trine VenusMars trine Venus: 18.5%18.5%Jupiter square MercuryJupiter square Mercury: 18.3%18.3%Mercury square VenusMercury square Venus: 17.8%17.8%Mercury square SunMercury square Sun: 17.5%17.5%Mars square SunMars square Sun: 17.5%17.5%Mercury square MoonMercury square Moon: 17.5%17.5%Source: AstroHot, 400 pairs on a fixed date grid, 1950–2050astrohot.com

Two people's planets are independent of each other, so the geometry sets the base rate: a square or trine with a 7° orb lands one way round in 7.78% of pairs and either way round in about 15%. The top eight sit a little above that because they are the top of about sixty such counts, and with 400 pairs each count can drift by ±3.6 points.

The baseline

What does a random pair score?

The mean is 56.6 on our 0–100 scale, and 18% of random pairs reach 70 or more — the kind of number other calculators label strong compatibility.

Synastry scores of 400 random pairs, share in each band
Synastry scores of 400 random pairs, share in each band Scores ran from 14.1 to 100; the highlighted band holds the mean. Your result above is shown as a percentile of this spread. 0%15%30%0–10: 0%10–20: 0.8%20–30: 2%30–40: 8.5%40–50: 22.3%50–60: 28.5%28.5%60–70: 19.8%70–80: 13.8%80–90: 2.5%90–100: 2%0–1010–2020–3030–4040–5050–6060–7070–8080–9090–100Source: AstroHot, 400 pairs on a fixed date grid, 1950–2050astrohot.com

Scores ran from 14.1 to 100; the highlighted band holds the mean. Your result above is shown as a percentile of this spread.

How the score is built — and why you should distrust every version of it

An aspect is an angle between two points, and only five are counted here: conjunction (0°), sextile (60°), square (90°), trine (120°) and opposition (180°), each with an orb of 5 to 8 degrees. That part is standard and mechanical.

The scoring is not. There is no authority establishing that a Moon trine is worth more than a Saturn square, so every site invents a scale, and none of them publish it. Ours multiplies three numbers: the aspect weight, the importance of each point, and how exact the angle is. It is a defensible scale and it is still arbitrary — which is exactly why the percentile matters more than the score. A relative position survives a change of scale; an absolute percentage does not.

What synastry cannot do

No inter-chart aspect has ever been shown to predict relationship outcomes. The frequencies on this page are the honest antidote: if the aspect being sold to you as a soulmate marker appears in a fifth of random pairs, it is not identifying your person, it is identifying a common angle between two slow-moving planets.

What the technique is genuinely good for is naming a friction you had not put words to. A chart that says “one of you needs reassurance faster than the other offers it” is a useful prompt whatever produced it. Use it that way, and check both birth times before you take the ascendant contacts seriously.

Sign compatibility The simpler sign-to-sign version, when you only have two star signs. Check your ascendant Before trusting ascendant contacts — see how much your birth time decides. One chart in full All placements and houses for a single birth date.

Cite this page

AstroHot. “Synastry Calculator: Two Charts, Scored Against a Baseline.” Accessed October 31, 2026. https://astrohot.com/synastry/

For Wikipedia {{cite web |title=Synastry Calculator: Two Charts, Scored Against a Baseline |url=https://astrohot.com/synastry/ |website=AstroHot |access-date=2026-10-31}}