Composite
Chart Calculator
Every planet in a composite chart sits at the midpoint between two people's positions: the composite Sun halfway between the two Suns, the composite Moon halfway between the two Moons. Astrologers read the result as one chart for the relationship.
What Is a Composite Chart?
A composite chart turns two birth charts into one. For every planet and point it finds the midpoint between the two people's positions and puts the composite planet there. The chart that results belongs to neither person, and astrologers read it as a chart of the relationship itself.
The technique spread in the 1970s. John Townley published The Composite Chart in 1973, generally cited as the first book on the subject, and Robert Hand's Planets in Composite (Para Research, 1975) gave delineations for the composite planets in each house and in aspect. Midpoints themselves are older: German astrologers of the Hamburg School worked with them from the 1920s.
No moment in the sky ever looked like a composite chart. Its planets can stand in arrangements a real sky never shows, and it has no birth time of its own to progress, although astrologers do follow transits to its points. That is the main difference from the Davison chart, which is cast for a real date and time.
⊕ Midpoint Method
Two Suns at 10° Aries and 10° Gemini give a composite Sun at 10° Taurus, halfway between them. The calculator repeats that step for the Moon and every other planet, both nodes, Chiron, Lilith, Juno, Ceres, Pallas, Vesta, the Vertex and the Lot of Fortune.
☌ Read as a Chart
The composite is interpreted with the same rules as a birth chart, with the relationship in place of a person: its Sun as what the pairing is for, its Moon as how it handles feeling and routine, its Ascendant as how others see the pair.
Sources
- John Townley on the origins of the technique: “Composite Charts, with Originator John Townley”, The Astrology Podcast, episode 128.
- Robert Hand, Planets in Composite: Analyzing Human Relationships, Para Research, first published 1975 (Open Library record).
How the Calculator Builds the Composite
The calculator first casts both birth charts with the API's ephemeris, after converting each local time to Universal Time, and asks the API for Whole Sign houses. It then pairs up the 20 points the two charts share and takes the midpoint of each pair along the shorter arc. Here is the API's function, cut to its working lines:
def _midpoint_longitude(lon_a, lon_b):
diff = (lon_b - lon_a) % 360
if diff > 180:
diff -= 360
return (lon_a + diff / 2) % 360Positions at 350° and 10° therefore give 0°, not 180°. Only when two positions are exactly 180° apart is neither arc shorter; the code then keeps the difference at 180 and returns the first person's position plus 90°, so the order in which the two people are entered decides the answer.
The rule matters most for near-oppositions. If two Moons are 179° apart, the composite Moon lands on one side of the zodiac; an error of a few hours in one birth time can push the gap past 180° and send it to the opposite point. A composite planet built from a pair that is close to opposite is only as reliable as the birth times behind it.
Each composite planet also gets the mean latitude and mean daily speed of its two parents, and it is marked retrograde when that average speed is negative. Because each planet is averaged on its own, the composite can show what a real sky cannot. Mercury is never more than about 28° from the Sun, yet when two Suns are close to opposite, two Mercuries can average to a point far from the composite Sun.
The angles come from the exact Ascendants and Midheavens. The composite Ascendant is the shorter-arc midpoint of the two people's Ascendants, so it can fall at any degree, and the composite Midheaven is the midpoint of their two Midheavens. One check applies to the Midheaven. In every birth chart it lies in the half of the zodiac above the horizon, less than 180° back from the Ascendant. Two shorter-arc midpoints taken separately can break that relation; when they do, the API takes the Midheaven midpoint on the longer arc, the point opposite, which puts it back above the composite horizon. In the worked example both angles use the shorter arc.
Houses are where programs differ most. With the Whole Sign houses the calculator requests, the first house is the whole sign that holds the composite Ascendant, starting at 0° of that sign, and each following house is the next sign. The Ascendant keeps its own degree inside the first house, and the Midheaven need not fall in the 10th; the 9th and 11th are common. The results page labels the system “Whole Sign (Composite)” and counts each planet's house by sign.
Other conventions are in use. Some programs work in Placidus and take the midpoint of each pair of natal cusps, which is also what this API does when asked for Placidus houses; for the pair below that puts the 2nd cusp at 23°27′ Aquarius and the 3rd at 9°48′ Aries, where Whole Sign starts those houses at 0°00′ Aquarius and 0°00′ Pisces. Others average only the Midheavens and work out the Ascendant and cusps from that point for the latitude of a chosen place, usually where the couple lives, which can change the rising degree and even the rising sign. All agree on the planets. Aspects within the composite use the orb table the site applies to single charts, listed on the methodology page.
Worked Example: Building the William–Harry Composite
The two charts used across this site's relationship pages: Prince William, born at 9:03 PM BST on June 21, 1982, and Prince Harry, born at 4:20 PM BST on September 15, 1984, both in London, with times from the official birth announcements. As with every example here, the point is the method, not a reading of two real people.
| Point | Prince William | Prince Harry | Apart | Composite | House |
|---|---|---|---|---|---|
| Sun | 0°06′ Cancer | 22°56′ Virgo | 82°50′ | 11°31′ Leo | 8th |
| Moon | 4°57′ Cancer | 21°20′ Taurus | 43°37′ | 13°09′ Gemini | 6th |
| Mercury | 8°58′ Gemini | 5°12′ Virgo | 86°14′ | 22°05′ Cancer | 7th |
| Venus | 25°39′ Taurus | 17°42′ Libra | 142°02′ | 6°41′ Leo | 8th |
| Mars | 9°12′ Libra | 16°57′ Sagittarius | 67°44′ | 13°04′ Scorpio | 11th |
| Jupiter | 0°29′ Scorpio | 3°33′ Capricorn | 63°04′ | 2°01′ Sagittarius | 12th |
| Saturn | 15°30′ Libra | 12°50′ Scorpio | 27°20′ | 29°10′ Libra | 10th |
| Uranus | 1°29′ Sagittarius | 9°52′ Sagittarius | 8°23′ | 5°41′ Sagittarius | 12th |
| Neptune | 25°32′ Sagittarius | 28°39′ Sagittarius | 3°07′ | 27°06′ Sagittarius | 12th |
| Pluto | 24°09′ Libra | 0°33′ Scorpio | 6°23′ | 27°21′ Libra | 10th |
| North Node | 13°19′ Cancer | 29°37′ Taurus | 43°42′ | 21°28′ Gemini | 6th |
| Ascendant | 27°28′ Sagittarius | 11°24′ Capricorn | 13°55′ | 4°26′ Capricorn | 1st |
| Midheaven | 2°27′ Scorpio | 17°03′ Scorpio | 14°36′ | 9°45′ Scorpio | 11th |
- The Sun, step by step. Written as longitudes counted from 0° Aries, Prince William's Sun (0°06′ Cancer) is 90.1061° and Prince Harry's (22°56′ Virgo) is 172.9489°. The difference B − A is 82°50′, less than 180°, so it stands. Half of it, 41°25′, added to Prince William's Sun gives 131.5275°, which is 11°31′ Leo. The far midpoint, 11°31′ Aquarius, is never used.
- The widest pair. The two Venuses are 142°02′ apart, the largest gap among the planets in this pair of charts. The shorter arc is the one through the signs between them, so composite Venus is 6°41′ Leo; the point opposite, 6°41′ Aquarius, lies on the longer arc and is not used. As a gap approaches 180°, the two arcs become nearly equal and the choice between them gets fragile.
- The Moon. The two Moons, 4°57′ Cancer and 21°20′ Taurus, are 43°37′ apart, and the composite Moon falls at 13°09′ Gemini. It stands 58°22′ from the composite Sun, so the two form a sextile (1°37′ from exact), one of the 51 major aspects inside this composite chart.
- The angles. Prince William's Ascendant is 27°28′ Sagittarius and Prince Harry's 11°24′ Capricorn, 13°55′ apart, so the composite Ascendant is 4°26′ Capricorn. Their Midheavens, 2°27′ Scorpio and 17°03′ Scorpio, give a composite Midheaven of 9°45′ Scorpio. That shorter-arc midpoint already sits above the composite horizon, so the Midheaven needs no correction.
- Houses. With Capricorn rising, Whole Sign houses make Capricorn the 1st house from 0°00′ Capricorn, and the cusps run 0°00′ Aquarius, 0°00′ Pisces and so on round the zodiac. The Midheaven at 9°45′ Scorpio falls in the 11th house rather than the 10th, which Whole Sign allows. Counting signs from Capricorn, the composite Sun (11°31′ Leo) is in the 8th house. Composite Mercury is 19°26′ from the composite Sun and Venus 4°50′, both within the distances a real chart allows, as expected when the two natal Suns are far from opposite (82°50′ apart).
The tightest major aspects between composite planets:
| Composite planets | Aspect | Positions | Orb |
|---|---|---|---|
| Neptune–Pluto | Sextile | 27°06′ Sagittarius / 27°21′ Libra | 0°15′ |
| Venus–Uranus | Trine | 6°41′ Leo / 5°41′ Sagittarius | 1°00′ |
| Sun–Mars | Square | 11°31′ Leo / 13°04′ Scorpio | 1°33′ |
| Sun–Moon | Sextile | 11°31′ Leo / 13°09′ Gemini | 1°37′ |
| Saturn–Pluto | Conjunction | 29°10′ Libra / 27°21′ Libra | 1°49′ |
Aspects between the slow planets, such as Saturn to Pluto, come largely from the birth years: anyone born in those years has similar positions, so they turn up in many composites. A reading would start with the composite Sun's sign, house and aspects, then the Moon and the Ascendant, which are personal to this pair.
Key Composite Placements
☉ Composite Sun
The center of the chart: what the relationship is for and what it is known by. Its sign, house and aspects carry the most weight in a composite reading. As the midpoint of two Suns on the shorter arc, it always lies within 90° of each person's own Sun.
☽ Composite Moon
How the relationship handles feeling, comfort and daily routine. The Moon moves fastest, so the composite Moon is the placement most exposed to an uncertain birth time: two hours' error in one chart moves it by about half a degree, and by far more if the two Moons are close to opposite.
♀ Composite Venus
What the pair enjoys together, how affection is shown and what each person values in the other. Astrologers look at its aspects to the composite Sun and Moon first. A composite Venus far from the composite Sun is a product of averaging, not of the sky.
♄ Composite Saturn
Where the relationship carries rules, obligations and long-term commitments. Saturn spends about two and a half years in a sign, so for two people born within a couple of years of each other the composite Saturn sits close to both natal Saturns, and many pairs of the same ages share its sign.
Composite, Davison or Synastry?
A composite averages positions and never asks when or where. The Davison chart answers that question with a real date, time and place halfway between the births, and synastry skips the merging altogether. The comparison table on the Davison page sets the three side by side and lists this example's composite and Davison positions planet by planet.
Composite Sun Through the Signs
The composite Sun's sign comes from both Suns. Two Suns in the same sign always give a composite Sun in that sign. Suns in opposite signs give one of the two signs square to them, depending on whether the gap is just under or just over 180°. Below, the twelve signs as astrologers commonly read them for the center of a relationship.
♈Composite Sun in Aries
A composite Sun in Aries describes a relationship organized around starting things. The pair is most recognizable when it is beginning something: a project, a move, a contest. Astrologers reading this placement ask how the two share the lead, since Aries has little patience for waiting on each other, and whether the relationship has anything to do once the new thing is under way.
♉Composite Sun in Taurus
With the composite Sun in Taurus, the relationship is defined by what it builds and keeps: property, a shared budget, a long habit of meeting in the same place. It is read as steady and slow to change. The usual caution is inertia, where arrangements that suited the pair years ago stay in place after they have stopped working for either person.
♊Composite Sun in Gemini
A Gemini composite Sun puts conversation at the center. Relationships with this placement are often described by how much the pair talks, writes or trades information, and it suits siblings, neighbors and colleagues as easily as couples. The weak point astrologers name is scatter: many plans made together, fewer finished, and a tendency to talk around a problem instead of settling it.
♋Composite Sun in Cancer
In Cancer the composite Sun turns the relationship inward, toward a household, a family or a small private circle. It suits partnerships that revolve around a shared home or around children. Readers of this placement look at who looks after whom and whether the care runs both ways, because the sign can let one person become the caretaker by default.
♌Composite Sun in Leo
A Leo composite Sun gives the relationship a public face: the pair is noticed together, and pride in the partnership is part of what holds it. The Sun is in its own sign here, which astrologers read as a clear sense of identity for the couple. The question they ask is whether both people get to be seen, or whether one stands in the other’s light.
♍Composite Sun in Virgo
Composite Sun in Virgo describes a working relationship in the plain sense: the pair does things, fixes things and keeps track of things. Shared routines, health habits and a fair division of labor sit at its center. The risk astrologers point to is that correction becomes the main way the two speak to each other, and praise goes unsaid.
♎Composite Sun in Libra
Libra corresponds to the seventh house of the natural zodiac, so a composite Sun here makes the partnership itself the subject: fairness, agreements, a shared social life, how the pair looks to others as a pair. The difficulty astrologers flag is avoidance, where keeping the peace matters more than saying what is wrong, and resentment builds quietly.
♏Composite Sun in Scorpio
A composite Sun in Scorpio is read as a relationship with high stakes: joint money, things kept private from everyone else, a strong sense of loyalty and an equally strong sense of betrayal. Readers watch how the pair handles control and trust. Scorpio relationships are described as hard to leave and hard to take lightly, for better and worse.
♐Composite Sun in Sagittarius
With the composite Sun in Sagittarius, the relationship is defined by movement and belief: travel, study, faith or politics, shared or argued over. The pair often needs a common direction more than a common address. Astrologers caution that the relationship can depend on the next plan, and that ordinary weeks with nothing ahead feel flat to both people.
♑Composite Sun in Capricorn
A Capricorn composite Sun describes a relationship built for the long term and judged by results: a business, a career one partner supports, a standing in the community. It is read as reliable and serious. The caution is that duty crowds out affection, and that the pair shows warmth mainly in private, if at all, while presenting a united front.
♒Composite Sun in Aquarius
In Aquarius the composite Sun points to friendship, shared causes and an arrangement that may not look like anyone else’s. The relationship often includes a wider group of friends or colleagues. Astrologers read it as needing space for each person’s independence; the risk they name is distance, a pair that agrees on ideas but rarely talks about feelings.
♓Composite Sun in Pisces
A composite Sun in Pisces is read as a relationship held together by sympathy, imagination or a shared ideal: music, faith, caregiving, a cause bigger than the two people. Its weak point is vague terms. What each person expects is rarely said out loud, so disappointment arrives without a clear cause, and the pair can drift rather than decide.
Frequently Asked Questions
What is a composite chart in astrology?
A chart made from two birth charts by taking the midpoint of each pair of positions: the composite Sun halfway between the two Suns, the composite Moon halfway between the two Moons, and so on for every planet and point. It is read as the chart of the relationship. This calculator takes each midpoint along the shorter arc, puts the composite Ascendant at the midpoint of the two exact Ascendants and counts Whole Sign houses from that Ascendant's sign.
How is the composite Ascendant calculated?
As the midpoint of the two exact Ascendants along the shorter arc, the same rule as for the planets. In the worked example 27°28′ Sagittarius and 11°24′ Capricorn give 4°26′ Capricorn. The composite Midheaven is the midpoint of the two Midheavens, here 9°45′ Scorpio. With Whole Sign houses the first house is the whole of the Ascendant's sign, so the house cusps sit at 0° of each sign while the Ascendant keeps its own degree, and aspects to it are measured from that degree.
Which midpoint does the calculator use when two planets are almost opposite?
Always the one on the shorter arc. At 179° apart that midpoint lies on one side of the zodiac; at 181° it is the point opposite. At exactly 180° neither arc is shorter, and the formula adds 90° to the first person’s position. Because a small change in a birth time can flip the result by 180°, composite planets built from near-oppositions deserve less weight.
Why can composite Mercury or Venus be far from the composite Sun?
In a real chart Mercury stays within about 28° of the Sun and Venus within about 47°. A composite averages each planet on its own, so when the two Suns are close to opposite, the composite Sun can land on one side of the zodiac while the two Mercuries or Venuses average to the other. The calculator reports what the arithmetic gives; astrologers read such placements with caution.
Why does another site give a different composite chart for the same two people?
The planets should match any program that takes shorter-arc midpoints of accurate birth-chart positions, and so should the Ascendant and Midheaven of a program that averages the exact angles. The houses often will not. This calculator uses Whole Sign houses; other programs take the midpoint of each pair of Placidus cusps, or work the Ascendant and cusps out from the composite Midheaven for a chosen place, which moves the rising degree as well. If the planets themselves differ, check both birth times and time zones.
Can a composite chart be made for more than two people?
Not with this calculator, which takes exactly two charts. Some astrologers build group composites by averaging three or more positions, but with more than two there is no single shorter arc to follow, and the conventions vary between programs. Pairs are easier to check, so for a family or a team, comparing two people at a time is the more transparent route.
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