Free synastry calculator with a composite chart
This free synastry calculator lays two birth charts side by side. It lists every aspect between one person’s planets and the other’s — conjunctions, oppositions, trines, squares and sextiles, each with its exact orb — shows whose planets fall in whose houses, and builds the composite chart: one chart made from the midpoints of each pair of planets, drawn as a wheel.
You can use it with or without birth times. Without a time the Moon is taken at noon and the houses and angles are left out, so you still see the planet-to-planet contacts. A sidereal (Lahiri) setting serves Vedic users; for the traditional Vedic guna score, use the kundli matching page instead. All of this is for tradition and entertainment, not prediction or advice.
How to use the Synastry & Composite Chart Calculator
- Under Person A and Person B, enter a name if you like, the Date of birth, Time of birth and Birth place; tick Birth time unknown when needed.
- Choose the Houses system, the Zodiac (tropical or sidereal Lahiri) and the Orbs (standard or tight).
- Read the number of aspects and the composite Sun and Ascendant at the top, then switch between the Synastry bi-wheel and the Composite chart.
- Go through the aspect list (closest first), the aspect grid, the house overlays and the composite positions.
- Download the wheel as SVG or PNG, or Copy as text.
Synastry & Composite Chart Calculator features
Inter-chart aspects with stated orbs
Ten planets, the North Node, Ascendant and Midheaven of each chart compared both ways, the closest aspect per pair, orb shown to a hundredth of a degree.
House overlays
Each person’s planets placed in the other person’s Placidus, whole-sign or equal houses.
Midpoint composite chart
Shorter-arc midpoints for every planet and angle, composite houses and aspects, and a downloadable wheel.
Bi-wheel
Person A inside, person B outside the zodiac ring, with lines for the flowing and challenging aspects between them.
No birth time needed
Planet aspects still work; the tool says what is left out and why.
How synastry aspects and orbs work
An aspect is a set angle between two points on the zodiac. In synastry one point comes from each chart. The tool measures the shorter arc between every pair and keeps the closest aspect within the orb. The orbs below are stated so you can compare results with other software; “tight” halves them.
| Aspect | Angle | Orb | Traditional nature |
|---|---|---|---|
| Conjunction ☌ | 0° | 8° | blending |
| Opposition ☍ | 180° | 8° | challenging |
| Trine △ | 120° | 6° | flowing |
| Square □ | 90° | 6° | challenging |
| Sextile ⚹ | 60° | 4° | flowing |
| With the Sun or Moon | — | +2° | |
| With the Node, Ascendant or Midheaven | — | −2° |
How the composite chart is calculated
The midpoint composite chart takes each planet in both charts and finds the point halfway between them along the shorter arc. Example: one Sun at 0°12′ Taurus and the other at 5°45′ Pisces are 54°27′ apart, so the composite Sun sits 27°13′ from each, at 2°58′ Aries. The composite Midheaven is the midpoint of the two Midheavens; each composite house cusp is the midpoint of the matching cusps, kept on the side that preserves the order of the houses. That composite Ascendant can differ by a few degrees from methods that rebuild houses from the composite Midheaven for a place.
Positions come from the same engine as the birth chart calculator, checked against published charts to about 2 arc-minutes. For the timing side of Saturn in one chart, see the Saturn return calculator.
Synastry & Composite Chart Calculator FAQ
Is this synastry calculator free?
Yes, with no sign-up. Both charts and the composite are computed in your browser, and the birth data never leaves it.
Can I use the synastry calculator with no birth time?
Yes. Tick Birth time unknown: planets are taken at noon, the Moon is marked as approximate, and houses, the Ascendant and the composite Ascendant are left out.
What is a composite chart?
A single chart for the relationship made from the midpoints of the two people’s planets and angles. It is read as a chart of the pair, not of either person.
Is there a Vedic synastry option?
Choose Sidereal (Lahiri). Both charts shift back by the ayanamsa, so most aspects stay the same; because the ayanamsa grows by about 50″ a year, partners born decades apart shift by a few tenths of a degree relative to each other and an aspect at the edge of its orb can appear or drop out. Whole-sign house overlays can change. Vedic compatibility is usually judged by guna milan in kundli matching.
Why do other sites show different aspects?
Mostly different orbs, a different list of points, or a different birth time zone. The orbs here are printed under the tables.
Does synastry tell us whether a relationship will work?
No. Astrology has no demonstrated predictive power. Treat the chart as tradition, conversation and fun, not prediction or advice.