Synastry chart calculator: the grid, the composite, and when it activates

The grid, with the orbs showing

A pair is two saved charts. Each side of the grid exposes the Sun, the Moon, Mercury through Pluto, the Ascendant and the Midheaven, and every cell where two of those points sit within three degrees of a conjunction, sextile, square, trine or opposition becomes a row — with the orb printed to three decimals, because the difference between a half-degree square and a two-and-a-half-degree one is the whole reading. There is no synastry-specific orb ladder and no wider allowance for the luminaries: the orb is the one the rest of the product states, so a contact that counts here is a contact that would count anywhere in the app.

A chart without a birth time is handled the way the rest of the product handles it. Its Ascendant and Midheaven rows are left out entirely, because noon angles are arbitrary, and its Moon rides as approximate — flagged, shown faded, and never counted as confirmed, since a noon Moon can sit about six and a half degrees either side of the true one. The grid is symmetric: computing it from either side gives the same rows, so a pair computes it once.

Whose planets land in whose houses

The Overview also lays each person’s planets into the other’s houses, in both directions, using the house system set on the account — Whole Sign by default, Placidus if that is the preference. The overlay exists only where it honestly can: a host chart without a birth time has no houses to overlay into, so that direction is absent rather than guessed.

The composite, and how it was cast

The composite is a midpoint chart: for every planet pair, the midpoint of the shorter arc between the two positions, with the composite Ascendant and Midheaven taken as the midpoints of the two charts’ angles and whole-sign houses counted from that composite Ascendant. The wraparound case is handled correctly — the midpoint of 29° Pisces and 1° Aries is 0° Aries, not 15° Libra — and the method is printed on the page, because a wheel that does not say how it was cast is false precision. Angles and houses appear only when both charts carry a birth time; a composite horizon built from one real angle and one noon guess would be neither.

Timing: when the sky touches the relationship

This is the part a grid cannot show. Every interaspect has two endpoints, one in each chart, and a transiting planet within orb of either endpoint activates it. The engine derives those activations from the two charts’ ordinary transit scans — no separate astronomy — and merges a transit that sits on both endpoints at once into one activation with both sides filled, rather than two half-stories. Each activation is weighted the way the pressure model weights a contact: the transiting body’s class, times a raised-cosine falloff of its peak orb over the three-degree envelope. Pluto on an exact endpoint weighs more than Mars a degree off, for the same stated reasons it does everywhere else in the product.

Because activations overlap continuously across a year, the Timing view does not rank them one by one. It stacks their weights into a density over time — the same shape as the pressure curve, deliberately, so a reader who can read one can read the other — and the strongest runs of that density become the ranked activation windows on the band. Any window expands back into the contacts that produced it, with their orbs and peak dates. Below the band, two pressure timelines are stacked, one per chart, sharing a single window: move the frame and both charts move together.

Cycles side by side

The Cycles view puts both charts’ long-period cycles — Saturn returns, Jupiter returns, the nodal cycle, retrograde windows, eclipses — on one horizontal axis, five years back and fifteen ahead, and highlights the spans where two windows share dates. An overlap is a description of the calendar: these two windows coincide. It is never a claim about what the coincidence does.

The report

A pair can be exported as a PDF that prints the same grid, composite, activation windows and cycle overlaps the tabs render, over a timeframe you choose — the next two weeks, month or quarter, this calendar year, the past month, or a custom range. It is read from the same surfaces, so the file and the screen cannot disagree.

What it does not do

There is no compatibility score. Two charts are not summed into a percentage, and no contact is labelled good or bad; the aspect names, the orbs and the dates are the reading, and the interpretation stays with the two people who know the relationship. Names are labels only — a nickname is fine — and neither a pair’s names nor its birth data ever rides on any usage event.

Trying it

Pairing and the Overview — the grid, the overlays, the composite — are free, and a free account holds two charts, which is exactly one pair. The Timing, Cycles and Report views are part of Pro, with a preview of seven days either side of today on the timing surfaces; Pro opens the full range, up to twelve months ahead, day by day, and holds up to ten saved charts.