How we calculate

Where the planets come from

Positions are worked out with Astronomy Engine, an open-source astronomy library. We use the tropical zodiac and geocentric positions, which means the sky as seen from the centre of the Earth. That’s the usual choice in Western astrology.

A chart shows the Sun, the Moon, Mercury to Pluto, and the Moon’s nodes, both true and mean. We don’t calculate Chiron or other asteroids, so you won’t find them here.

How we check the results

We compared the planets on 39 test charts from 1879 to 2026 with JPL Horizons, NASA’s public data on the solar system. The largest difference was 18.3 arcseconds, about 1/200 of a degree. Rising signs, house cusps and nodes were compared with the Swiss Ephemeris, a standard tool in astrology. The test charts are made up for testing, and none of them belongs to a real person.

You can try this yourself. The Check our math section on the homepage shows how to look up the Sun’s position in Horizons and compare it with ours.

Birth places and clock times

A chart needs the exact moment of your birth, so we have to know what the clocks in your town said that day.

• Places come from GeoNames, which lists towns around the world with coordinates and time zones.
• Clock rules come from the IANA Time Zone Database, the record that computers around the world use.
• Zone borders come from OpenStreetMap data, used to check the time zone for a place.

Clock records from before 1970 aren’t complete. When a date is uncertain, your chart says so. An hour’s error moves your rising sign and houses, while your planets barely change. If clocks changed at the hour you were born, the chart tells you how it read that hour.

Houses, and charts without a birth time

You can choose between two house systems, Placidus and Whole Sign, and the chart always names the one in use. Placidus can’t be worked out very far north or south, so in those places the chart uses Whole Sign and tells you.

If you don’t know your birth time, you still get your planets. We leave out the rising sign, houses and Moon aspects, because they depend on the hour. If a planet changed sign that day, you’ll see both signs.

The calculator works for dates from 1800 to 2199.

What the words are based on

The meaning lines in a birth chart are fixed. There’s one line for each of the ten planets in each of the twelve signs, 120 in all, and two people with Venus in Leo read the same line. They follow the traditional meanings of each planet and sign.

Horoscopes start from the calculated sky for that day, week or month. Before a reading goes up, an automatic check compares the planets, signs, aspects and dates it mentions with the calculation, and a reading that doesn’t match isn’t published. The check can’t judge everything: how long a mood might last, for example, is outside what it reads. Each reading shows the sky behind it, so you can look for yourself.

Your card of the day comes from all 78 cards. We shuffle once a day, using the date, and deal one card to each sign from Aries to Pisces. Nobody picks the cards, and hard cards come up as often as any other. Your number is where the Moon is, counted from your sign.

Every reading shows its date. If the newest one is older than today, the page says so.

The same house rules apply to all the text here. It doesn’t predict bad events or promise results, it doesn’t try to frighten you, and it gives no medical, legal or financial advice. The 120 chart lines also pass an automatic check for banned wording and repeated phrases.

What the numbers can’t tell you

Astronomy can show where a planet was on the day you were born. It can’t show that the planet has anything to do with your life, and science hasn’t found that it does. We check the sums as hard as we can, and we offer the meanings as a way of thinking about yourself. The disclaimer says more.

The outside data and code we use are listed on the credits page.

Last updated October 30, 2026.