Astrology synastry: overlays, aspects, composite, and Davison
Synastry here is two natal charts placed on each other. It is not a sign-pairing slogan. Both birth instants and both places have to be real before any overlay means anything.
- English name
- Synastry
- Also calculated
- Composite midpoint chart · Davison chart
Editorial review: 2026-09-22 · Reviewed by fateshow · Editorial method
Synastry
Relationship type changes which houses are highlighted and how the reading is ordered. It does not change a single calculated number.
Concept snapshot
Input
Two birth instants and two birthplaces
What is calculated
House overlays, inter-aspects, composite, Davison
Scenes
Overall, romantic, marriage, business, family, friendship
What it is not
A compatibility percentage
What the comparison is
Each person already has a tropical chart. Synastry asks where one person’s planets fall in the other’s houses, and which aspects form between the two sets of planets. The same Venus in the 5th house and in the 12th house are different placements. Only the overlay shows which one you have.
A composite chart joins midpoint longitudes into a chart of the relationship itself. Houses there use equal house, because a composite Ascendant does not force another house system’s cusps. A Davison chart is the chart of the midpoint in time and the midpoint in place: one real instant and one real location, so its houses and aspects are internally consistent.
What fateshow calculates
Inter-aspects print the angular separation, the orb, and whether the aspect is applying or separating. Allowances used on the chart are 8° for conjunction and opposition, 7° for trine and square, 4° for sextile, and 1.5–2.5° for minor aspects, widened by 1° when the Sun or Moon is involved.
Five themes — emotional bond, communication, attraction and tension, stability, growth and space — list which inter-aspects landed in them and how many are easy or tense. They do not become a score. Choosing romantic, marriage, business, family, friendship, or an overall view only reorders emphasis. Recalculating with another relationship type must reproduce the same positions.
What it is not
It is not Vedic kuta scoring, BaZi day-master combination, or a Zi Wei palace mirror. Those comparisons live on their own pages because the objects are different.
A missing birth time on either side removes that person’s angles. Do not borrow the other person’s Ascendant to fill the gap.
Safety boundary
Overlays describe a structure between two charts. They are not medical, legal, or financial advice, and they do not decide whether two people should stay together.
Common mistakes
- Reading a sun-sign match as if the house overlay had been calculated.
- Treating the relationship-type switch as a change in the numbers.
- Quoting a composite house cusp without saying equal house was used.
Use it in fateshow
Frequently asked questions
Which relationships can this page describe?
Overall, romantic, marriage, business, family, and friendship. The type is a lens. The positions stay the same.
What is the difference between composite and Davison?
Composite midpoints the longitudes. Davison midpoints the two birth moments and the two places, then casts an ordinary chart for that instant and location.
Is there a match score?
No. Themes count aspects. They do not add up to a pass mark.
Sources and editorial basis
- 1. fateshow tropical synastry rules
Supports house overlays both ways, inter-aspects with the orbs above, the equal-house composite, and the Davison midpoint in time and place. Relationship type does not enter the arithmetic.