Composite vs Davison Chart, and Where Coalescent Fits

Published 23 September 2026 · Updated 1 October 2026

Composite, Davison and Coalescent all take two birth charts and return one chart for the relationship. They are built by three different methods, and on the same couple they can disagree about which sign the Sun is in, which house it falls in, and which planet runs the whole chart.

This article works all three on one real pair so you can see exactly where they line up and where they part company. It follows on from the guide to Synastry, Draconic and Uranian, which covers the other family of relationship readings, the ones that keep both charts intact.

The one-line difference

The Composite is a construction, an average of numbers. The Davison is an actual moment of sky. That single distinction explains most of what follows.

The worked example

Every figure below comes from one pair, John Lennon and Yoko Ono, whose birth data has long been published: 9 October 1940 at 18:30 in Liverpool, and 18 February 1933 at 20:30 in Tokyo. Using one couple throughout means the differences you see belong to the methods.

All three charts here use the tropical zodiac and Placidus houses, the report's defaults. That matters because the house system changes where the Composite and Davison planets land, and you can change it at the top of the report.

Composite: the average chart

For each body, take the two natal longitudes and find the point halfway between them on the shorter arc. Lennon's Sun sits at 16°16' Libra, Ono's at 29°23' Aquarius, and the halfway point is 22°49' Sagittarius. Do that twelve or thirty times and you have a full chart.

The angles are handled the same way. The two Midheavens, 7°03' Capricorn and 9°21' Cancer, average out to 8°14' Libra, and the house cusps are then built from that Midheaven the way any chart is built. This matters: the Ascendant is derived from the composite Midheaven, it is not the average of the two natal Ascendants. Averaging the Ascendants directly would put this couple's Ascendant at 14° Cancer, which would leave the Midheaven sitting at the bottom of the wheel. For this pair the two approaches land in exactly opposite signs, which is a good illustration of why the derived version is the one to use.

What it reads as: the psychological tone of the relationship, its shared temperament, what the two of you become when you are in the same room. It has no date and no place, so it does not move and there is nothing in it to time.

Davison: a real chart for a real moment

The Davison averages the two births themselves, then casts an ordinary chart for the result. Halfway between 9 October 1940 and 18 February 1933 is 14 December 1936, at 14:30 UT. Halfway between Liverpool and Tokyo is roughly 44°33' north, 68°21' east, a point in southern Kazakhstan. The chart is then cast for that moment at that spot, using the same ephemeris and the same house system as any birth chart.

What it reads as: the relationship's path over time, how it develops and where it is going. Because it is a dated chart, this is the one to use when you want timing.

Where the two agree, and where they do not

On this couple, eight placements land in the same sign in both charts: Sun in Sagittarius, Mercury in Capricorn, Saturn in Pisces, Uranus in Taurus, Neptune in Virgo, Pluto in Cancer, Chiron in Gemini and the North Node in Sagittarius. The Sun agrees to within half a degree, 22°49' against 22°27'.

Then look at the angles.

The Ascendants are in opposite signs. The Midheavens are in opposite signs. Jupiter is on the far side of the wheel. And the same Sun, in the same degree of the same sign, is a hidden twelfth-house Sun in one chart and a visible fifth-house Sun in the other. Read those two sentences about a couple and you would not think you were reading about the same people.

The reason is structural. The Composite averages two longitudes and knows nothing at all about the seven years between the two births. The Davison puts each planet where it actually was at the midpoint moment, after however many circuits it made in between. Those two answers coincide only when a planet's total travel between the births happens to land close to a whole number of circuits plus the separation. For this couple the Sun does. Jupiter does not, and it ends up 165 degrees away from where the Composite puts it.

The angles diverge for a simpler reason. The Composite Midheaven is the average of two Midheavens, and a Midheaven is set by clock time. Averaging a 1940 evening in England with a 1933 evening in Japan produces a number, and that number has no connection to where the Midheaven really was on any day. The Davison Midheaven is the real one for 14 December 1936 at 14:30. There was never any reason for them to match.

Practical consequence: trust sign and aspect agreement between the two charts, and treat the houses and angles as two separate readings. The report's Composite vs Davison tab is built for exactly this, listing the placements that repeat in both so you can see which themes are confirmed twice.

Coalescent: what it is, and what can honestly be said about it

The Coalescent chart takes a different route. For each pair of positions it measures the shorter arc between them, divides 360 by that arc to get a harmonic number, then multiplies one of the positions by that harmonic. Each body therefore gets its own harmonic, which is what separates this from an ordinary harmonic chart. The result is the same whichever partner you start from, which is a genuine property of the arithmetic and not a convention.

Both of the worked examples given in the original published description of the method reproduce exactly in this report, including the awkward one where the two positions straddle 0 degrees Aries.

Worked on the same Suns: Lennon at 16°16' Libra and Ono at 29°23' Aquarius are 133°07' apart, so the harmonic is 2.70, and the Coalescent Sun comes out at 20°48' Virgo. Not Sagittarius, where both of the other charts put it. A different sign, a different element, a different reading.

Two things are worth knowing before you read one.

Where it comes from. The method was published in 1996 as a short monograph, Coalescent Horoscopes: A New Method of Synastry, by Lawrence Grinnell (who wrote as Dhruva) and David Dukelow, from ACS Publications. Dukelow also wrote a companion technical paper for the same publisher giving the arithmetic and its worked examples, and that paper is where the formula below comes from. It is calculated the same way in mainstream astrology software and on the large free chart sites. It is the youngest and the least used of the three, and far less has been written about what its placements mean, so you will find plenty on a Composite Venus and almost nothing on a Coalescent one.

The method amplifies small errors. Multiplying by a harmonic multiplies uncertainty by the same factor, and then some, because an error in one position also changes the arc and therefore the harmonic itself. Some measured examples from this couple:

• Move one birth time by 30 minutes and the Coalescent Moon shifts about 9 degrees.
• Move it by 10 minutes and the Coalescent Moon shifts about 3 degrees, which is more than most people's whole orb allowance.
• The natal Moon in that half hour moved about a quarter of a degree. The Coalescent version of it moved thirty times further.

It gets sharper when two positions are close together. Two people whose Suns are 10 degrees apart produce a harmonic of 36, and one degree of difference in either Sun, about one day of birth date, swings the Coalescent Sun through 80 degrees. Below one degree of separation the formula has no sensible answer at all and the calculation falls back to the plain midpoint. The method's own literature reaches the same conclusion from the other direction and says so plainly: where a pair of natal positions sits closer than about twelve degrees, the coalescent result for that body may need to be set aside.

The houses work differently here too, and this part is by design. A merged chart has no obvious place to be cast for, so the method specifies the Meridian house system, which is built from the Midheaven alone and needs no location at all. The cusps are forced from the Coalescent Midheaven, which is itself a harmonic figure, so the Ascendant and the houses carry the same amplified uncertainty as everything else. The original description carries its own warning here, that once the coalescent cusps crowd together, both birth times have to be right before the house placements mean anything.

What is it read for? The method's own description points at two things: an unusual responsiveness to transits, and something essential in the connection that the other charts do not reach, the reason two people are together underneath the circumstances that brought them together. Read it for that, as one more layer on a relationship alongside the synastry and the composite.

Which one to run

Start with the Composite. It is the one most readings are written for, most of the material you will find online assumes it, and it answers the question people usually mean when they ask about a relationship chart. Add the Davison when you want timing, because it is the only one of the three that can be progressed.

All three are calculated together in the free Composite, Davison and Coalescent report, so running one gives you all of them and you can compare them the way this article does. It is free, it takes two sets of birth data, and the settings it used are printed at the top of the page so you can change them.

Transits and progressions to a relationship chart

Both charts take transits. The Composite sits at fixed degrees, so a transiting planet crossing its Venus or its Descendant is read the same way it would be in any chart, and plenty of astrologers work this way.

Where the Davison pulls ahead is that it has a real birth moment behind it. That makes it a chart you can progress, and it gives transits to it a natal footing the Composite does not have.

The Composite has no date, so it cannot be progressed in the ordinary way. What is used in its place is the progressed composite, which progresses each partner's chart first and then builds the composite from the progressed positions. It is a separate report and it answers a separate question: how the shared chart is changing as the two of you change.

What none of the three will tell you

Whether the relationship lasts. A hard Composite does not mean a short relationship, and an easy one does not mean a happy one. These charts describe the shape of the thing, they do not forecast the outcome.

Who is responsible for what. All three merge the two charts, so neither person survives in the result. If you want to know whose Saturn is landing on whose Moon, that question belongs to synastry, where both charts stay intact.

Anything reliable from guessed birth times. The Composite Ascendant, the Davison houses and the whole Coalescent chart all depend on the birth times being right. If either time is approximate, read the planets and the aspects and leave the houses alone. Our guide to finding or rectifying a birth time covers what to do about it.

Related guides

• Synastry, Draconic or Uranian?, the other family of relationship reports, the ones that keep both charts separate.
• How to read a synastry chart, a section by section walkthrough.
• How to choose your chart settings, which matters here because the house system you pick changes the Composite and Davison house placements.