✧ Free Decan Calculator
Umbriel's free decan calculator finds which decan (which ten-degree third of a sign) your Sun, Moon and Rising sign fall in, and the rulers each decan is given in the modern and the old Chaldean schemes, from your birth date, time and place.
Free, no account, no email. Runs in your browser.
14160+ people cast their chart here in the last 30 days.
No account, no email. The Sun's decan usually needs only the date.
TRADITIONALA traditional technique: in the books before 1700.
- What you'll needBirth date (time and place for your Moon and Rising decans)
- What you getYour Sun, Moon and Rising decans, each decan's sub-sign and ruler in the modern scheme, its ruler in the Chaldean faces, and the exact degree each sits at
- CostFree, no account required
What a decan is
Every zodiac sign is 30° wide, and a decan is one third of it: 0° to 10°, 10° to 20° or 20° to 30°. Twelve signs of three make thirty-six decans. Your Sun's decan is the one most people mean when they ask "what decan am I", and it splits each Sun sign into three: an early, a middle and a late Aries, and so on.
Deeper.a cup-of-tea read
Decans are older than the zodiac signs as we use them. Egyptian astronomers told the hours of the night by thirty-six star groups rising one after another, about ten days apart, and when Hellenistic astrology took over the twelve signs it kept the thirty-six as ten-degree slices, called faces. Each face was given a planet in the Chaldean order (Mars, the Sun, Venus, Mercury, the Moon, Saturn, Jupiter) starting from 0° Aries.
Modern astrologers mostly use a second scheme instead, which gives each decan a sub-sign of the same element: the first decan of a sign is that sign itself, the second is the next sign of its element, the third is the one after. A Leo's second decan is sub-ruled by Sagittarius and Jupiter, the third by Aries and Mars. The same pattern is the Indian drekkana. Umbriel gives both schemes and names which is which.
How Umbriel computes it
Deeper.a cup-of-tea read
Umbriel computes the Sun, the Moon and the Ascendant for your birth moment, reads the sign as the longitude divided by 30, and the decan as the degree within the sign divided by 10. The modern sub-sign is the sign itself, four signs on or eight signs on (the same element); its ruler uses the modern rulers, so Scorpio's is Pluto, Aquarius's Uranus and Pisces's Neptune. The Chaldean face is the planet at that place in the repeating order of seven, counted from the first face of Aries. The Sun moves about a degree a day, so its decan changes roughly every ten days and the date settles it except on the day it crosses 10° or 20°; the Moon changes decan every eighteen hours or so, and the Rising sign every forty minutes, so those need the time.
What's in your result
Deeper.a one-breath read
- Your Sun decanWhich third of your Sun sign you were born in, to the degree.
- Moon and Rising decansThe same for the Moon and the Ascendant, where the birth time allows.
- The modern sub-sign and rulerThe sign of the same element that colours each decan, and the planet that rules it.
- The Chaldean faceThe older planetary ruler of each ten degrees, from the Hellenistic and medieval books.
- The exact degreeSo a placement that sits on a decan's edge can be seen as one.
Don’t know your birth time?
Deeper.a cup-of-tea read
Know it roughly? Give the time and say where it came from (a certificate, a parent’s memory, or something rough like “early morning”), and your chart tells you what could change within that window.
Don’t know it at all? Umbriel does not fill the gap with a guess. Tick “I don’t know the time at all” and it checks your whole birthday, hour by hour, then tells you two things: which placements are the same whatever time you were born, as exact as they would be if you knew the minute, and which are down to two signs, both named, so you know what a parent’s memory would settle.
The Ascendant, the Midheaven and the houses are left out rather than approximated. A birth time is the one thing they cannot be computed without, and an approximate Rising sign that looks exact is worse than no Rising sign at all.
Common questions
What decan am I?
Your Sun decan comes from the degree of your Sun: 0° to 10° of your sign is the first decan, 10° to 20° the second, 20° to 30° the third. Because the signs do not start on the same calendar day every year, a date table can be a day out; Umbriel computes the Sun's real degree for your birth.
What are the dates of each decan?
Roughly the first ten days of a Sun sign are its first decan, the next ten the second and the last ten the third. The exact days shift by a day or so from year to year, which is why the calculator works from your birth year rather than a fixed table.
What is the difference between the modern decans and the Chaldean faces?
The modern scheme gives each decan a sub-sign of the same element, with that sign's ruler. The older Chaldean faces give each ten degrees a planet in the repeating order Mars, Sun, Venus, Mercury, Moon, Saturn, Jupiter. They often disagree, and Umbriel shows both.
Do I need my birth time for my decan?
Not for the Sun, unless it crossed 10° or 20° on your birthday. The Moon's decan changes about every eighteen hours and the Rising sign's about every forty minutes, so those two need the time.
Are decans the same as cusps?
No. A cusp birth is one near the edge of a whole sign; a decan is a third of a sign. A Sun at 29° is in the third decan and also near the cusp of the next sign, and Umbriel says when a placement sits within a degree of an edge.
Is this decan calculator free?
Yes: all three decans and both sets of rulers, with no account and no email, calculated in your own browser.
What if I don’t know my birth time?
Umbriel checks your whole birthday hour by hour and separates what is certain from what is not. Placements that are the same whatever time you were born are shown as exact. Placements that changed sign during the day are shown as two named signs, so you know what a parent's memory would settle. The Ascendant, Midheaven and houses are left out rather than approximated. They cannot be computed without a time, and an approximate Rising sign that looks exact is worse than none.
Do I need an account or an email address?
No. There is no sign-up, no email capture and no free trial. Enter your details and the result is drawn in your own browser.
Go deeper
A decan is a third of a sign. Each sign's own page is the whole of it.
Related free tools
Next doorDegree Image CalculatorUmbriel's free degree image calculator finds the exact degree of every placement in your chart and which of its own 360 images each one takes. The first image is open; the rest are part of Membership.Prints in the head of this page, all public domain except where stated: the planets and signs of the zodiac send down their influence on the body of a man, engraving, 17th century, Wellcome Collection; Urania's Mirror, Sidney Hall, 1825, Library of Congress via Wikimedia Commons; Astrolabe, Iran Isfahan, Qajar dynasty (1786–1925), Late 18th century with later additions, Art Institute of Chicago. Ground: Andreas Cellarius, Harmonia Macrocosmica, 1661, Wikimedia Commons.
Further down the page: the Egyptian zodiac, coloured engraving by J. Chapman after V. Denon, Wellcome Collection. The next-door print comes from that page's own head. The pointing hand: a pointing hand, after a medieval manuscript margin (line art by Jerimee).
Umbriel offers every system here as a set of prompts to think with, never as a statement of fact about who you are. Take what's useful, leave the rest.