Private astrology calculator

Compare two birth charts

A synastry chart lays one person's planets over the other's and reads the aspects between them; enter both birth cities and times and every cross-aspect, overlay and reading is computed here, offline.

Two birth moments

Enter both birth details

Pick each birthplace — the zone follows.

Person A

Birth place

An offline city list. Nothing goes online.

Set the place manually

Coordinates are optional here. A recognized IANA time zone (for example Europe/Warsaw) is enough to apply the correct historical offset, but the rising sign and houses need latitude and longitude too.

Birth date
Birth time

Pick a city to apply its time zone

Person B

Birth place

An offline city list. Nothing goes online.

Set the place manually

Coordinates are optional here. A recognized IANA time zone (for example Europe/Warsaw) is enough to apply the correct historical offset, but the rising sign and houses need latitude and longitude too.

Birth date
Birth time

Pick a city to apply its time zone

Both birth moments and coordinates stay in this tab.

Ready when both people's details are entered.

The Chart Between YouOne chart for a pairing — the midpoint, or a real Davison sky.Cast the chart →carries your moment as Person AThe Sky Over Yours, TodayWhich planets are touching your chart now — and when each contact is exact.See today's sky →carries date · time · cityThe Sun's ReturnYour solar return for any year, cast wherever you will be.Cast your return →carries date · time · city

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Direct answer

What you need

Both people's birth dates and times are required. Each city's zone and coordinates apply on their own — without one, that person's house overlays are left out.

Nothing is uploaded or placed in the URL. A cast is kept only in this tab's own memory — long enough for "Read next" — until you close the tab.

Method & limits

Astronomy first, symbolism second.

Cross-aspects use the same documented orbs as every other chart on this site and are never reduced to one overall number. A person whose birth time is unknown still gets their Sun and planet signs; only their own houses, angles and both house-overlay lists are left out.

Frequently asked questions

What is a synastry chart?

A synastry chart overlays two people's birth charts on top of each other and reads the aspects — the angles — between one person's planets and the other's. It also places each person's planets into the other's houses, when both birth times and places are known, showing where the two charts' rhythms line up tightly or only loosely.

Why isn't there a single rating for how well two charts fit?

This page shows the specific aspects between two charts — which planets connect, by how many degrees, and how tightly — because those are measurable facts about angles in the sky. Collapsing all of that into one overall number would claim more precision than the underlying astronomy actually supports, so every result here stays broken out by the individual aspect you can read for yourself.

What happens if one person's birth time is unknown?

Leaving one person's birth time unknown still calculates their planets' zodiac signs and the aspects between the two charts, using a neutral midday placeholder for that person. What gets hidden is that person's houses and chart angles, along with both house-overlay lists below, since neither can be calculated responsibly without a real clock time for that birth.

What do the house overlays mean?

A house overlay places one person's planets into the houses of the other person's chart, showing which areas of that person's life — relationships, home, career and so on — the other person's planets fall into. Reading it both directions shows how each person's planets land in the other's houses, which is different information from the aspects between their planets alone.

Which orbs does this synastry chart use?

Cross-aspects use the same orb set as every other chart on this site: eight degrees for a conjunction or opposition, six for a square or trine, and five for a sextile. In the list below, aspects wider than three degrees are folded out of view by default; the wheel is looser, hiding only the aspects wider than five degrees.

Is either person's birth information sent anywhere?

No. Both charts are calculated entirely in your browser, using the same local astronomy library and offline city list as every other calculator on this site. Neither birth date, time or place is uploaded, stored on a server, or placed in the page URL — there is no link that could ever reveal either person's birth details.