House Overlays: Whose Planets Land in Whose Houses
A house overlay places one person's already-computed planet into the other person's twelve houses — not their own. That single word, "other's," is the whole mechanism this page is about: which chart's houses a point is checked against, why that direction can succeed for one person and find nothing for the other, and what has to be true about a birth time before either direction runs at all.
This page describes the mechanism only — the containment check, the direction, and what does or does not run when a birth time is inexact. What a placement in a given house traditionally means for two specific people is a separate, interpretive question this page does not answer.
What a house overlay actually computes
Every chart in this system carries twelve house cusps, drawn by the Placidus method used everywhere else on this site, and a house overlay takes one person's point — an exact ecliptic longitude, computed the same way as any other natal position — and checks which of the other person's twelve Placidus cusp-to-cusp arcs it falls inside. That check carries no orb: an aspect only counts within a stated orb of an exact angle, but a house overlay has none at all. A longitude either falls inside a given arc or it does not; there is no near-miss result the way there is for an aspect that lands just outside its allowed range.
Because the check runs against the OTHER person's cusps, not the point-holder's own, the same two charts produce two structurally different computations: one person's ten points checked against the other's twelve houses, and — separately — the second person's ten points checked against the first person's. These use two different sets of house cusps, so one direction placing a point inside a given house of one chart says nothing about where that person's matching point falls in the other chart.
Both directions, computed independently
A pair reading runs the same overlay calculation twice: once placing the first person's points into the second person's houses, and once placing the second person's points into the first person's — two separate calls, each with the two charts swapped, and neither depending on the other's result.
That independence is also why a reading can end up one-way. Each direction only needs the houses of the person being checked AGAINST to be usable — not the houses of the person whose points are being placed. If one person's birth time is exact and the other's is not, the direction that checks against the exact-time person's houses still runs in full, while the other direction is dropped rather than approximated.
Why a direction runs, or does not
Houses need an exact, known birth time
A direction's houses count as usable only when that person's birth time is both known and recorded as exact — not a noon default, not an approximate guess. Fall short of that, and this system does not estimate cusps from a guessed time: the entire direction into that person's houses is left out of the reading, returned as no overlays at all rather than a lower-confidence set of them. A reading built from one exact birth time and one approximate one can therefore carry real overlay placements in one direction and none in the other, and the reading's own notes record that omission rather than leaving the asymmetry unexplained.
A surviving placement can still carry a caveat
Once a direction does run, one further, narrower flag can still apply to a single placement inside it: the same Moon-only rule used elsewhere in this system marks a placed Moon as time-sensitive when the person supplying that placement's birth time is unknown, because the Moon moves roughly a degree every two hours — fast enough to change houses within a single morning. That flag qualifies one placement; it does not remove it, and none of the other nine compared bodies is singled out this way.
Ten bodies, twelve houses, up to two directions
The same ten bodies compared for aspects elsewhere in this system — Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto — are the ten checked for house overlays. Each one has a single computed longitude, and a single longitude falls inside exactly one of twelve houses, so one direction can produce at most ten overlay placements — one per body — and a full two-way reading, with both birth times exact, produces at most twenty placements in total, ten each way.
Two things this page deliberately leaves out
Two names in the underlying weighting data that no overlay reaches
The internal table this system uses to weigh a house overlay also carries entries for the North Node and Chiron, alongside the ten bodies above. Neither one is ever passed into an overlay calculation today — every live pair reading uses only the same ten-body list used for aspects — so those two entries currently describe a placement this product does not produce, not one it quietly includes.
What a house or a placement traditionally means
Traditional astrological convention reads each of the twelve houses as a different broad area of life — the same convention behind calling the first house self-presentation or the seventh partnership — but that reading is an inherited convention, not something this engine computes from a birth time and place. This page does not carry a paragraph of authored interpretation for any specific house or placement; that is a different kind of content this product deliberately leaves to an astrologer, the same boundary drawn on this product's other synastry pages.
What landing in a house does not mean
Does a planet in the seventh house mean partnership?
The containment check answers one question and only one: which of twelve arcs a longitude falls into. Tradition attaches meanings to those arcs — the seventh to partnership, the eighth to what two people share and hide — and the check itself attaches none. Those meanings are interpretive convention rather than measurement, they are not predictive, and no overlay computed here forecasts what two people's future together holds.
Where this page hands off to an astrologer
Which chart's houses are read, in which direction, and what happens when a birth time is inexact — that is the extent of what is settled here. Reading a particular planet in a particular house is authorship, and this page does not attempt it.
See this layer applied inside a full synastry reading
House overlays are one part of what a full synastry reading checks between two people, alongside the aspects described elsewhere on this site.