Decans in astrology, and what each ten days is doing
A decan is a ten degree slice of a zodiac sign, about ten days long. Three decans per sign, twelve signs, thirty six in a year. Your decan is decided by whether your birthday falls in the first, middle or last ten days of your sign.
Decans split every zodiac sign into three, which turns twelve seasons into thirty six. It is the most useful idea in astrology that almost nobody explains properly.
The full table of all thirty six decans, with dates and rulers, is further down. If that is all you came for, skip ahead.
A season having its own beginning, middle and end
The zodiac came from people watching the same year happen over and over. Twelve slices of one solar cycle, each describing what a stretch of the year actually feels like based on the light and the weather that arrives with it.
The problem with twelve is that a month is a long time. The light in the first days of a season and the light at the end of it are measurably different. Late August does not feel like the third week of September. The year does not change character on a switch, it moves through a beginning, a middle and an end, and then it hands off to the next thing.
That is the whole concept behind decans. Everything else is bookkeeping.
How to find your decan in ten seconds
Decans are counted from the start of your sign’s season, so count the days.
- Decan 1, the first ten days of your sign, roughly the 22nd or 23rd of one month to the 1st or 2nd of the next.
- Decan 2, the middle ten days, roughly the 1st or 2nd to the 11th or 12th.
- Decan 3, the last ten days, roughly the 11th or 12th to the 21st, 22nd or 23rd.
The dates shift by up to a day depending on the year, because the sun does not cross those degrees at the same clock time every year. Leap years move them most. If your birthday sits right on a boundary, the only way to know for certain is to have your chart calculated, because it comes down to the hour the sun crossed that degree in your birth year.
Which decan system this table uses, and why it matters
This trips people up constantly, because two different traditions both use the word decan and they do not agree.
The triplicity decans, which is what I use
Every sign belongs to an element, and every element has three signs in it. The first decan of a sign is ruled by that sign’s own ruler. The second and third are ruled by the rulers of the other two signs in the same element, taken in zodiac order.
Virgo is earth, and earth is Taurus, Virgo, Capricorn. So Virgo decan 1 is Mercury, Virgo’s own ruler. Decan 2 hands to Capricorn, so Saturn. Decan 3 hands to Taurus, so Venus. Three flavours of the same sorting instinct: gather it, systematise it, keep what is worth keeping.
The Egyptian or Chaldean faces
The older system, and the one you will find in traditional and horary texts. It ignores elements entirely and runs the seven visible planets in Chaldean order, starting with Mars on the first decan of Aries and continuing around the whole wheel without resetting. It produces completely different rulers, and it is not wrong, it is answering a different question.
Both traditions are genuinely old. If you want the long version of where they came from, Wikipedia traces decans from Egyptian star clocks through to the Hellenistic systems.
If a book gives you a decan ruler that does not match the table below, that is why. Neither of you made a mistake. Check which system it is using before you assume one of them is broken.
All 36 decans, with dates
Dates are the range the start falls in across recent and coming years. The sub-ruler column uses the triplicity system explained above. The last column is what that stretch of the year is actually doing, which is the part you will not find on other decan pages.
| Decan | Dates, approximate | Degrees | Sub-ruler | What the year is doing |
|---|---|---|---|---|
| Aries 1 | Mar 19 or 20 to Mar 29 or 30 | 0 to 10° | Mars | The first move. Nothing is built yet, and that is the point. |
| Aries 2 | Mar 29 or 30 to Apr 9 | 10 to 20° | Sun | The push. The start has to survive its own second week. |
| Aries 3 | Apr 9 to Apr 19 or 20 | 20 to 30° | Jupiter | The overreach. Speed meets the first real resistance. |
| Taurus 1 | Apr 19 or 20 to Apr 29 or 30 | 0 to 10° | Venus | The landing. What got started finally gets a body. |
| Taurus 2 | Apr 29 or 30 to May 9 or 10 | 10 to 20° | Mercury | The tending. Slow, unphotogenic, the part nobody posts. |
| Taurus 3 | May 9 or 10 to May 20 or 21 | 20 to 30° | Saturn | The enjoying. Peak green, and the first pull toward wanting more. |
| Gemini 1 | May 20 or 21 to May 30 or 31 | 0 to 10° | Mercury | The looking out. Too many inputs and all of them interesting. |
| Gemini 2 | May 30 or 31 to Jun 10 | 10 to 20° | Venus | The gathering. Collecting hard, committing to nothing. |
| Gemini 3 | Jun 10 to Jun 20 or 21 | 20 to 30° | Saturn | The overload. Nearly full light and still nothing chosen. |
| Cancer 1 | Jun 20 or 21 to Jul 1 | 0 to 10° | Moon | The turn. Longest light, and it starts shortening that same day. |
| Cancer 2 | Jul 1 to Jul 11 or 12 | 10 to 20° | Mars | The interior. Warmth with something protective underneath it. |
| Cancer 3 | Jul 11 or 12 to Jul 22 | 20 to 30° | Jupiter | The holding. What you have quietly decided to keep close. |
| Leo 1 | Jul 22 to Aug 1 or 2 | 0 to 10° | Sun | The display. Confidence with real heat behind it. |
| Leo 2 | Aug 1 or 2 to Aug 11 or 12 | 10 to 20° | Jupiter | The heat. Sustained, and starting to cost something. |
| Leo 3 | Aug 11 or 12 to Aug 22 or 23 | 20 to 30° | Mars | The last full week. Fullness that already knows it is ending. |
| Virgo 1 | Aug 22 or 23 to Sep 1 or 2 | 0 to 10° | Mercury | The noticing. Out of the fullness, the first thing you see is the mess. |
| Virgo 2 | Sep 1 or 2 to Sep 11 or 12 | 10 to 20° | Saturn | The labor. Noticing becomes work, or it turns into self-attack. |
| Virgo 3 | Sep 11 or 12 to Sep 22 or 23 | 20 to 30° | Venus | What you keep. The sort resolves, and it runs into the equinox. |
| Libra 1 | Sep 22 or 23 to Oct 2 or 3 | 0 to 10° | Venus | The even hour. Day and night level, and the calculation switches on. |
| Libra 2 | Oct 2 or 3 to Oct 12 or 13 | 10 to 20° | Saturn | The review. Balance stops being automatic. |
| Libra 3 | Oct 12 or 13 to Oct 22 or 23 | 20 to 30° | Mercury | The decision. The pretty part ends and something has to be chosen. |
| Scorpio 1 | Oct 22 or 23 to Nov 1 or 2 | 0 to 10° | Mars | The drop. What is going is going, and there is no pretending left. |
| Scorpio 2 | Nov 1 or 2 to Nov 11 or 12 | 10 to 20° | Jupiter | The dissolve. Grief, dreams, letting go of the shape of it. |
| Scorpio 3 | Nov 11 or 12 to Nov 21 or 22 | 20 to 30° | Moon | What you protect. You find out what you carried through. |
| Sagittarius 1 | Nov 21 or 22 to Dec 1 or 2 | 0 to 10° | Jupiter | The distance. Looking well past the immediate dark. |
| Sagittarius 2 | Dec 1 or 2 to Dec 11 or 12 | 10 to 20° | Mars | The belief. Meaning gets built precisely because evidence is thin. |
| Sagittarius 3 | Dec 11 or 12 to Dec 21 | 20 to 30° | Sun | The last stretch before the floor of the year. |
| Capricorn 1 | Dec 21 to Dec 30 or 31 | 0 to 10° | Saturn | The floor. Longest night, and the light turns back the same week. |
| Capricorn 2 | Dec 30 or 31 to Jan 9 or 10 | 10 to 20° | Venus | The build. Cold, structural, and completely unrewarded. |
| Capricorn 3 | Jan 9 or 10 to Jan 19 or 20 | 20 to 30° | Mercury | The endurance. Winter with no novelty left in it. |
| Aquarius 1 | Jan 19 or 20 to Jan 29 or 30 | 0 to 10° | Saturn | The step back. Seeing the whole system from outside it. |
| Aquarius 2 | Jan 29 or 30 to Feb 8 or 9 | 10 to 20° | Mercury | The difference. Naming what you will not go back to. |
| Aquarius 3 | Feb 8 or 9 to Feb 18 | 20 to 30° | Venus | The forecast. Planning a spring you cannot feel yet. |
| Pisces 1 | Feb 18 to Feb 28 | 0 to 10° | Jupiter | The thaw. Edges soften and definition drops. |
| Pisces 2 | Feb 28 to Mar 9 or 10 | 10 to 20° | Moon | The blur. Everything at once and none of it fixed. |
| Pisces 3 | Mar 9 or 10 to Mar 19 or 20 | 20 to 30° | Mars | The last of the old year. Emptying out before the first move. |
Calculated from the Swiss Ephemeris across 2024 to 2040 and given as ranges, because every one of these boundaries moves by up to a day depending on the year.
Your sign tells you which season. Your decan tells you where in it you arrived.
Three decans are three jobs, not three grades
Notice that the three decans of a sign are not “a bit Virgo, quite Virgo, very Virgo.” They are three different jobs inside one season.
Virgo 1 notices. Virgo 2 does the work. Virgo 3 decides what survives. Same sign, three genuinely different assignments, and most people only ever get described by the middle one.
What a decan tells you
The texture of the stretch of year you were born into. Whether the season was still opening, in full swing, or handing over. That shows up as a real difference in how people who share a sign operate, and it is why two Scorpios born three weeks apart can feel like they have almost nothing in common.
What it does not tell you
What happens to you. Nothing in astrology does. This is pattern recognition across the solar cycle, not prediction, and anyone selling you the second thing with a decan attached is selling you something else.
It also does not override your chart. Your sun’s decan is one line of a very long document. Your moon, your rising, and the houses everything lands in will all argue with it, and they should.
Decans are a calendar you are living in right now
The part almost nobody does. Decans are not only a birth chart lookup.
Decans give you a ten day window instead of a thirty day one. Whatever today’s date is, the sun is in one of these thirty six windows. That window has a character, and it holds for about ten days. Reading the current decan rather than the current sign gives you a much sharper read on why a particular week feels the way it does, because ten days is close enough to a real timescale to be useful and a month is not.
This is exactly the logic a Season Map runs on, just applied to one specific chart instead of the general year. Six pages, twelve seasons scored, the weeks that are heavy and the months that hold nothing, with real dates.
Keep reading
Questions people actually ask
Is a decan the same as a cusp?
No, and decans and cusps get mixed up constantly. A cusp is the boundary between two signs, which is a real astronomical moment but a very short one. A decan is a ten day span inside a sign.
Do decans apply to the moon and rising sign too?
Yes. Every planet sits at a degree, and every degree falls in a decan. The sun’s decan is just the one people ask about because it is the one their birthday gives them.
Why do the decan dates move each year?
The solar year is not exactly 365 days, so the sun crosses each degree at a slightly different clock time each year and the calendar corrects with leap days. Every boundary moves by one day at most.
Which of the decans is the strongest?
None of them. That question comes from treating signs as a ranking, which they are not. Decan 1 is the most recognisably that sign because it is the season opening at full strength.
What are the three decans of each sign ruled by?
Under the triplicity system, the sign’s own ruler first, then the rulers of the other two signs of the same element, taken in zodiac order. The full list is in the table above.
How do I know which of the decans I am?
Find the start date of your sign and count. First ten days is decan 1, middle ten is decan 2, last ten is decan 3. If you are within a day of a boundary, have your chart calculated.
Want your own year mapped out like this?
A Season Map is six pages built from your birth chart. It lays your year out as a calendar: the weeks that are loaded, the months that hold nothing at all, with real dates. It costs nothing and I write them by hand.
You are on the list.
Your Season Map is being written by hand, so give it a few days. It lands from Jakayla at cosmicallycreated.com, so keep an eye out for that name.