What Decan Am I? How to Find Your Decans From Your Birth Chart

← Back to Zodiac Signs

"What decan am I?" usually means "which decan is my Sun in?", but every placement in a chart has a decan of its own. Your Sun, Moon, Mercury, Venus, Mars and the rest can each sit in a different third of their sign. Finding them takes one number per placement: the degree within the sign.

This page is the method. It shows where to read the degree, how the boundaries work, what to do when a position sits very close to 10° or 20°, and what you can and cannot know without a reliable birth time. For what decans are and how their rulers are assigned, see decans in astrology.

Note on what the site calculates. Astrologist.com explains decans as part of its educational library. The free birth chart gives you the sign, degree and minute of every placement, and that is the input for the steps below; the chart itself does not work out, name or show decans or decan rulers. The example figures were produced offline using the chart's own planetary code. The Astrologist chat can talk through placements you give it, but it does not compute decans for you.

Step 1: read the sign and degree

Open your chart and find a placement, for example the Sun. It is written as a degree and minute within a sign, such as 15°10' Capricorn. The first number is the whole degrees already travelled through that sign, from 0 to 29. The second is the arc-minutes, from 00 to 59, with sixty minutes to a degree.

Use the degree within the sign, not the total longitude around the zodiac, and not a house number. Sign degrees and house cusps are different things: a house cusp is the degree where a house begins, which depends on birth time and place, as shown on how to find your house cusps. Decans are counted inside the sign only.

Step 2: apply the boundaries

Compare the degree and minute with the two boundaries at 10°00' and 20°00':

Each decan includes its starting point and stops just before the next boundary. A shorthand you will often see is 0°00' to 9°59', 10°00' to 19°59' and 20°00' to 29°59'. That shorthand works for positions shown in whole minutes, but the rule underneath is the exact longitude: a planet at 9°59'40" is still in the first decan, because it has not yet reached 10°00'. When a planet passes 29°59' it does not reach a 30th degree of the same sign; it moves to 0°00' of the next sign and into that sign's first decan.

Step 3: take care near 10° and 20°

Most placements are nowhere near a boundary, and the decan is clear at a glance. A position within a few arc-minutes of 10°00' or 20°00' needs more care, for two reasons.

The first is display precision. The free chart rounds each position to a hundredth of a degree, which is 36 seconds of arc, before showing it as degrees and whole minutes. A position a few seconds short of 10° can therefore be displayed as 10°00'. A displayed 10°00' or 20°00' is not, on its own, proof of which side of the line the exact position lies. This is a question of how many digits are shown, not an astrological allowance. There is no decan orb, and nothing on this site treats a planet as being "in two decans" because it is close to a boundary.

The second is birth time. Every placement moves, and a small error in the recorded time can move a fast body across a boundary. If a position sits right at 10° or 20°, the honest answer is that the decan depends on precise data: an exact, reliable birth time and a full-precision position from an ephemeris.

Step 4: repeat for each placement

Do the same check for the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Each has its own degree and its own decan, and they are independent of one another. Your Sun can be in the first decan of its sign while your Moon is in the third decan of a different sign.

The Ascendant also has a decan, read from its degree in the same way, but only when the birth time is reliable. The Ascendant moves through a whole sign in roughly two hours on average, and much faster or slower depending on the sign and latitude, so a decan of the Ascendant is one of the most time-sensitive placements in a chart. Ascendant degree vs rising sign explains how quickly that degree moves.

Worked example: Ruben

Ruben is the fixed example used across this site: born in London on 5 January 1993 at 12:00, taken here as a recorded birth time. His positions, recalculated with the free chart's planetary code, put his placements in these decans:

None of these sits within a degree of 10° or 20°, so the display precision question does not arise for this chart.

A few ruler examples show how the two conventions from the concept page read the same position differently. Ruben's Sun, in the second decan of Capricorn, falls in the face of Mars in the Chaldean convention, and in the decan associated with Taurus, ruled by Venus, in the triplicity convention. His Moon, in the first decan of Gemini, is in the face of Jupiter, or in the Gemini decan ruled by Mercury. His Ascendant, in the first decan of Taurus, is in the face of Mercury, or in the Taurus decan ruled by Venus. These are two separate conventions, not two parts of one answer. The complete list is on decan rulers.

When the birth time is unknown

Without a reliable birth time, the free chart calculates positions for an internal noon reference. That reference is a calculation convenience, never the moment of birth. Some decans can still be known from the date alone, and some cannot.

Running Ruben's date from 00:00 to 23:59 London time shows the difference, for Ruben's date only:

• Sun: 14°39' Capricorn at 00:00 and 15°40' Capricorn at 23:59, so the second decan of Capricorn all day.
• Moon: 29°03' Taurus at 00:00, in the third decan of Taurus. It entered Gemini, and the first decan of Gemini, at about 01:41, and reached 10° Gemini, the second decan, at about 19:35. It ended the date at 12°29' Gemini. So the Moon occupied three decans in two signs during one date.
• Ascendant: it passed through all twelve signs during the date, so its decan cannot be known without the time.
• Other planets: on this date Mercury to Pluto each stayed in one decan all day.

That pattern is typical but not guaranteed. The Sun's decan is often stable through a single date, but on a date when the Sun is close to 10° or 20° of its sign, it can change decan during the day. The Moon is the body most likely to change decan within a date, because it moves roughly 12° to 15° a day. Mercury, Venus, Mars and the other planets move more slowly, yet any of them can also cross a 10° or 20° line on the date in question, even when its sign does not change. If your birth time is uncertain, check the positions at the earliest and latest possible times rather than relying on the noon placement. How to read a chart without a birth time and birth chart without birth time cover the wider picture.

Why decan date lists are only approximate

Many websites list "decan dates" for each Sun sign, such as the first ten days of the sign. The Sun does spend roughly ten days in each decan, but the moment it crosses 10° or 20° shifts from year to year, and the calendar date of that moment depends on the time zone. The same applies to the start of each sign, which is why zodiac sign dates are given as typical ranges and why born on the cusp measures the change year by year. A list of decan dates is a rough guide at best. The degree in your chart is the answer.

What to do with your decans

Once you know your decans, the next step is to decide whether to use decan rulers and, if so, which convention. Decans in astrology explains the two conventions and why the site does not choose one for you, and treats a decan as a shading within the sign rather than a new sign or a personality type. To check your own degrees, open the free birth chart. The calculation choices behind those degrees are listed on the methodology page, and you can ask the Astrologist about a placement once you have its sign and degree.

Related articles

• Decans in Astrology
• Decan Rulers for All 12 Signs
• Born on the Cusp?
• Zodiac Sign Dates
• Ascendant Degree vs Rising Sign
• How to Read a Chart Without Birth Time
• Birth Chart Without Birth Time
• Zodiac Signs