How We Calculate Your Natal Chart

How Do We Turn Your Birth Details Into A Chart?

Your birth details are converted into a chart through a fixed pipeline: your birthplace is matched against the GeoNames database, your local birth time is converted to UTC with the IANA time zone database, planet positions are computed with Astronomy Engine, and our own code derives the Ascendant, Midheaven, house cusps, lunar node and Lilith from sidereal time.

Everything runs in your own browser. Nothing is sent to a server, and the chart itself is never computed on our side. You enter a first name if you want one, a birth date, a birth time and a birthplace. After the # sign in the page address, the browser keeps those details so you can bookmark your chart. Your Sun, Moon and Rising signs are remembered on your own device to power a "My Chart" shortcut.

The zodiac used is tropical: signs are measured from the March equinox, using the true ecliptic and equinox of date. The chart lists the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, the true North Node, mean Black Moon Lilith, the Ascendant, Midheaven, Descendant, IC and Part of Fortune.

How Is Your Birthplace And Birth Time Converted?

Your birthplace is looked up in the GeoNames list of places with 5,000 or more inhabitants, an open dataset published under a CC BY 4.0 license. Typing a city name gives you matches to pick from; the lookup returns the latitude and longitude that anchor the whole chart.

Your local birth time is then converted to UTC using the IANA time zone database built into your browser. This matters more than it sounds. Time zone rules have changed constantly over the decades, and the IANA database includes historical offsets, daylight saving changes and wartime time. A birth in 1943 in Europe, for example, may fall under a wartime offset that a naive lookup would miss.

The result is a single moment in UTC plus a fixed point on Earth. Every later step, from planet positions to house cusps, depends on that pair. Getting it right is what makes a chart from 1908 and a chart from 2028 come out equally sound.

How Are Planet Positions And Angles Calculated?

Planet positions come from Astronomy Engine, an open-source, MIT-licensed astronomy library. It corrects for light-time, aberration, precession, nutation and Delta T, the small adjustment that reconciles Earth's irregular rotation with uniform clock time.

The Ascendant, Midheaven, house cusps, lunar nodes and Lilith are computed by our own code. The chain runs through sidereal time: from your birth moment and location we compute local sidereal time, the angle of the sky relative to your horizon. The Midheaven is the ecliptic point exactly on that meridian; the Ascendant is the ecliptic point rising in the east. From there the house cusps follow.

The North Node is the true node, which wobbles with the Moon's actual motion, rather than the smoother mean node. Lilith is the mean Black Moon Lilith, the Moon's empty focal point, and it is shown to the whole degree because programs define that point slightly differently.

Which House System Does The Chart Use?

House cusps are calculated with Placidus houses by default, the most common system in modern Western astrology. Whole Sign and Equal houses are also available if you prefer to read your chart that way.

Placidus divides the sky by the time each degree of the ecliptic takes to travel between the horizon and the meridian, which is why it is sensitive to latitude. Above the polar circles it cannot be drawn at all, so for high-latitude births the chart falls back to Porphyry houses, which divide each quadrant into three equal arcs.

Without a birth time, the chart is calculated for noon and leaves out the Rising sign, the houses and the Midheaven entirely. The Ascendant moves about one degree every four minutes of clock time, so a wrong birth time is the biggest source of error in any chart, not the math. The Moon adds its own uncertainty: it moves about 12 to 15 degrees a day, so a noon Moon can be up to about 7 degrees off and may sit in a neighbouring sign.

How Are Aspects And Orbs Determined, And How Accurate Is The Result?

Aspects are the angular distances between pairs of points, and each is allowed a tolerance called an orb. The chart uses: conjunction at 0 degrees with an 8 degree orb, opposition at 180 with an 8 degree orb, trine at 120 with a 7 degree orb, square at 90 with a 7 degree orb, sextile at 60 with a 5 degree orb, and quincunx at 150 with a 3 degree orb.

Accuracy was tested in November 2026 against Swiss Ephemeris 2.10, the reference software behind most professional astrology programs. 300 random charts from 1900 to 2030 were recalculated. Planets agreed within 19 arcseconds, with the Sun within 3 and the Moon within 5. The Ascendant, Midheaven and every Placidus house cusp agreed within half an arcsecond, and the true North Node within 15 arcseconds. Mean Lilith differed by up to about 7 arcminutes, which is why it is shown to the whole degree. For scale, one degree is 3,600 arcseconds and a sign is 30 degrees.

What Are The Limits Of This Calculator?

The limits are factual: the site calculates tropical charts only, not sidereal (Vedic) charts. In 2026 the Lahiri ayanamsa used in Vedic astrology is about 24 degrees, so most placements in a sidereal chart fall one sign earlier than in a tropical chart. There is no Chiron and no asteroids.

Your birth time is the weak link. If it is off by twenty minutes, the Ascendant can move about 5 degrees, enough to change the Rising sign and shift house cusps. A missing time means no Rising sign, no houses and a noon Moon that may land in a neighbouring sign.

Two cautions on interpretation. Large language models such as ChatGPT can explain placements you give them, but they are not ephemeris software: asked to work out positions from a birth date, they can state wrong signs or degrees. Calculate the chart first, then ask about the listed placements. And astrology itself is a symbolic and reflective practice, not a science. Nothing here predicts events, health or money; the chart is a mirror for thinking, not a forecast. A deeper personal reading, written for one chart and one question at $10, is planned, with an email list to announce it.