Decan Calculator — Find the Face Lord of Every Placement

What a decan is

A decan, or decanate, is a band of ten degrees inside a sign. Since a sign spans thirty degrees, it holds three decans. Across all twelve signs there are thirty-six decans, and the ancients assigned a governing planet to each.

The decan lord is a second, subtler ruler sitting under the sign's main ruler. A planet in the middle decan of a sign is said to take on the tone of that decan's lord as well as the lord of the sign itself.

Decans reach back to Hellenistic and Egyptian astrology, and they still carry weight in Vedic practice, where the same divisions are called drekkana. They add resolution to a reading that thirty signs alone cannot give.

How the decan and its lord are found

We take each placement's degree within its sign and divide by ten. Degrees zero to nine fall in the first decan, ten to nineteen in the second, twenty to twenty-nine in the third. That fixes the decan number.

For the lord we follow the standard scheme in which a sign's three decans are ruled by the domicile lords of the three signs of the same element: the sign itself and its two trines, in zodiac order. Aries, a fire sign, takes the lords of Aries, Leo and Sagittarius, which are Mars, Sun and Jupiter.

Because this is generated from the classical domicile table, the whole thirty-six-face scheme follows with no hand-copied grid to drift. Cancer's decans come out as Moon, Mars, Jupiter; Taurus as Venus, Mercury, Saturn, exactly as the sources give them.

What you get back

Enter your birth data and the tool lists every placement with:

• Its degree and sign.
• Which of the three decans it occupies.
• The face lord ruling that decan.
• Where that face lord sits in your chart.
• The angles ASC and MC included in the table.

Reading your decan lords

Start where a planet's sign lord and its decan lord differ. The sign lord is the broad theme; the decan lord is a specific flavour running through it. A Sun in Leo always leans solar, but in Leo's second decan it also takes on Jupiter, warming and expanding the expression.

Then follow the face lord's own placement. If a planet's decan lord sits in a busy house or makes strong aspects, that colouring is played out in that part of life. A quiet, afflicted face lord says the same theme runs thinner.

The three decans also sketch a life-stage arc within the sign, an early, middle, and later face. Some readers use the first decan for the purest expression of the sign and the third for its most developed or complicated form.

Use decans as refinement, not verdict. They add a second ruler to weigh, and the finest detail only matters once the sign and house picture is clear.

A worked example: a London evening birth

Take the chart our verification script measures for 1 January 2000 at 17:30 UT in London. Read a few of its face lords to see the method in action.

The Sun sits in the first decan of Capricorn. Capricorn's first decan is ruled by Saturn, so the Sun's face lord is Saturn, which itself sits in Taurus. The Moon in the second decan of Cancer takes Mars as its face lord, Cancer's decans running Moon, Mars, Jupiter.

Mars falls in the third decan of Aquarius, which draws Jupiter as its face lord under the trine scheme, the same lord shared by the other Aquarius and Pisces placements that land in Jupiter-ruled faces here.

The Ascendant in late Cancer sits in the third decan of Cancer, so its face lord is Jupiter too, while the Midheaven in early Aries takes Mars as its first-decan lord. Each degree is reproduced by an automated check.

What this tool does not claim

Decan lordship is a traditional rulership scheme, not a physical measurement. The thirty-six faces are a symbolic layer, and their effects belong to interpretive practice rather than to anything demonstrated.

This page uses the element-trine assignment of face lords, the scheme shared across most classical sources. A minority of traditions order the faces by a strict Chaldean walk instead, so your face lords may read differently in those systems.

As always with degrees, an uncertain birth time can push a fast body or an angle across a ten-degree boundary and change its decan.

Decans beside signs and houses

Think of rulership in resolutions. The sign gives a coarse ruler over thirty degrees. The decan refines it to ten. The single-degree monomoiria, which some traditions extend from this same logic, divides the sign into thirty face-lord days.

Decans colour a planet, while the house still tells you the stage of life it acts on, and the aspects tell you who it talks to. Read all three together for a full picture.

Our method in one line

Each placement on sub-arcsecond astronomy (VSOP87/ELP via astronomy-engine) is assigned a ten-degree decan, and its face lord is generated from the classical domicile lords of the sign's element trines. The worked-example lords are reproduced by an automated check. Reviewed by Dr. Amara Osei, Astronomy Reviewer.