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.

Names (optional)

Shown in this page’s headings and remembered only on this device — never sent.

Person A

Birth place

City search runs on your device. Your search is not sent.

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

Loading chart tools…

Person B

Birth place

City search runs on your device. Your search is not sent.

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

Loading chart tools…

Both birth moments and coordinates stay in this browser.

Ready when both people's details are entered.

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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.

Inputs are not sent for calculation or placed in the URL. The details stay in this browser, which remembers them for next time unless you choose Don’t remember; saving birth details to an optional account is a separate choice.

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.

In short

Computes
The aspects between two people’s planets, and each person’s planets in the other’s houses.
You enter
Both birth dates, times and cities.
You get
A bi-wheel, a cross-aspect list with orbs and both house overlays; no single rating.
Accuracy
The same engine and orbs as every chart here: 8° conjunction and opposition, 6° square and trine, 5° sextile.

Checked

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. Inputs are not sent for calculation or placed in the URL. This browser remembers them on this device for next time unless you choose Don’t remember, and Forget removes them. Saving birth details to an optional account is a separate choice, and you can delete them.