Every house system starts from the same two facts: the degree rising in the east and the degree culminating overhead. What they disagree about is everything after that. Given those two points, how do you cut the rest of the chart into twelve?
There is no single answer, and the reason is geometric rather than philosophical. A birth chart is a flat drawing of a three dimensional situation, and there are several defensible ways to slice a sphere. Each system picks a different circle to divide, and once you know which circle a system divides, its behaviour stops being mysterious.
The Two Families
Almost every system belongs to one of two groups.
Sign based systems treat the zodiac itself as the thing being divided. The houses are cut from the ecliptic in tidy thirty degree portions. Whole Sign and Equal House are the two that matter.
Quadrant systems start from the Ascendant and Midheaven as fixed corners, then subdivide the four quarters between them. Because the quarters are almost never equal in size, quadrant houses are almost never thirty degrees wide. Porphyry, Alcabitius, Campanus, Regiomontanus, Placidus and Koch are all quadrant systems, and they differ only in what they divide and how.
That one distinction explains most of the differences you will notice in your own chart.
Whole Sign
How it works. The sign containing your Ascendant becomes the entire first house, the next sign is the whole second house, and so on. Houses and signs are the same twelve compartments. Your Midheaven still exists as a degree and can land in the ninth, tenth or eleventh.
Where it came from. It is the oldest system in the Western tradition, standard in Hellenistic astrology from roughly the first century BCE. Chris Brennan's Hellenistic Astrology treats it as the original method of the tradition rather than as one option among several. It fell out of Western use during the medieval period and was recovered in the late twentieth century through translation projects that put the Greek sources back into circulation.
Where it is used now. The traditional and Hellenistic revival, and Indian astrology, where the rasi chart has always worked this way.
What it is good at. Rulership is easy to follow, because each house has exactly one sign and therefore exactly one ruler. Nothing is ever intercepted. It works at any latitude, including inside the Arctic Circle where the quadrant systems fail.
Equal House
How it works. The first house begins at the exact degree of the Ascendant, and every house is thirty degrees from there. Same regularity as Whole Sign, but anchored to a degree rather than to a sign boundary.
Where it came from. Also ancient, and used alongside Whole Sign in the Greek material.
Where it is used now. A minority preference in modern Western practice, and popular among astrologers who want the Ascendant degree to genuinely begin the chart while keeping houses even.
The trade off. Like Whole Sign, the Midheaven floats and is read as a sensitive degree rather than as the tenth cusp.
Porphyry
How it works. The simplest quadrant method. Take the arc from the Ascendant to the Midheaven and cut it into three equal parts, then do the same for the other three quarters.
Where it came from. Third century, and the earliest quadrant system in the tradition.
Where it is used now. Rarely on its own, but it matters historically as the first attempt to make the Midheaven an actual house cusp.
Alcabitius
How it works. Divides the time it takes the Ascendant degree to rise to the Midheaven, rather than dividing space.
Where it came from. Named for the tenth century Arabic astrologer al Qabisi, and it became the standard through the medieval Arabic and Latin periods.
Where it is used now. Among astrologers working specifically with medieval material, who want the house division their sources actually used.
Campanus
How it works. Divides the prime vertical, the great circle passing through the east point, the zenith and the west point, into twelve equal parts, then projects those back onto the zodiac.
Where it came from. Campanus of Novara, thirteenth century.
Where it is used now. Uncommon, though it has advocates who like that it divides space around the observer rather than time.
Regiomontanus
How it works. Divides the celestial equator into twelve equal parts and projects them onto the ecliptic through great circles running to the north and south points of the horizon.
Where it came from. Johannes Müller of Königsberg, 1436 to 1476, the German mathematician whose Latin name gives the system its name. Anthony Louis gives the reasoning behind its adoption: Müller was aware of the quadrant systems already available, and proposed equatorial division on the argument that this was how Ptolemy would have done it. Ptolemy's authority in that period was close to absolute, so European astrologers took up Regiomontanus as standard. Morin de Villefranche called it the most rational house system ever invented.
Where it is used now. Traditional horary, and this is the important part. William Lilly cast his charts in Regiomontanus and tested every horary rule against Regiomontanus cusps. Christian Astrology, published in 1647, remains the foundation text of English horary, which means the entire rulebook was validated against this specific system.
Louis puts the consequence plainly: the empirical validity of Lilly's techniques rests on the use of Regiomontanus houses to identify significators, and nobody knows how his methods might have differed had he experimented with anything else. If you are doing horary out of Lilly, you are inheriting his house system along with his rules, and separating the two is not straightforward.
Placidus
How it works. Divides time rather than space. It takes the semi diurnal arc, the time a degree spends above the horizon, and cuts it into three, so the cusps mark where a point has completed a third and two thirds of its journey.
Where it came from. Placidus de Titis, a seventeenth century Italian monk and mathematician. It was not immediately dominant.
Why it became the default. Printing, more than merit. Placidus tables were the ones bound into the widely circulated nineteenth and twentieth century ephemerides, including Raphael's, so it became the system most astrologers had tables for. Convenience compounded into convention, and it is now the default in most astrology software.
Where it is used now. Most modern Western practice, natal and psychological.
Its weakness. Because it divides time, it degrades badly at extreme latitudes. Above roughly sixty six degrees, some degrees never rise or set and the mathematics breaks down.
Koch
How it works. Also time based, sometimes called the birthplace system. It uses the time it takes each degree to rise at the specific latitude of birth.
Where it came from. Walter Koch, mid twentieth century Germany, making it by far the youngest system in common use.
Where it is used now. Widely in German speaking astrology, and among astrologers who came up through cosmobiology and the Ebertin material. Some rectification workers prefer it because the intermediate cusps move quickly.
Its weakness. The same high latitude failure as Placidus, and for the same reason.
At A Glance
| System | Divides | Era | Typically used for |
|---|---|---|---|
| Whole Sign | The zodiac, by sign | Hellenistic, first century BCE | Traditional revival, Hellenistic, Indian astrology |
| Equal | The zodiac, from the Ascendant degree | Ancient | Modern minority preference |
| Porphyry | The quadrants, into thirds | Third century | Historical interest |
| Alcabitius | Rising time of the Ascendant degree | Tenth century | Medieval work |
| Campanus | The prime vertical | Thirteenth century | Uncommon |
| Regiomontanus | The celestial equator | Fifteenth century | Traditional horary, after Lilly |
| Placidus | The semi diurnal arc, by time | Seventeenth century | Most modern Western natal work |
| Koch | Rising time at the birth latitude | Twentieth century | German practice, cosmobiology, rectification |
Why A Planet Changes Houses Between Systems
Two reasons, and they are worth separating.
Sign based against quadrant. In Whole Sign, a planet is in the house that matches its sign, full stop. In every quadrant system, house size varies, so a planet near a boundary can sit in one house in Whole Sign and the previous one in Placidus.
Quadrant against quadrant. All the quadrant systems agree on the Ascendant and the Midheaven and disagree about everything between them, so the intermediate cusps move while the angles stay put. This is why switching from Placidus to Koch usually moves less than switching from Placidus to Whole Sign.
Nothing you switch will change your rising sign, your Sun sign, or any aspect between planets. Aspects are measured between degrees and do not use houses at all.
Intercepted Signs
In quadrant systems a sign can fall entirely inside a house without appearing on any cusp. That is an interception, and it happens more often at higher latitudes where house sizes get more uneven. Sign based systems cannot produce them, because every sign is a house.
Modern astrologers have developed psychological readings for intercepted signs. Those readings are not part of the older house doctrine, so treat them as a specific school's technique rather than as a universal fact.
So Which One Should You Use?
Start with what you are doing, because the tradition has already answered this by branch.
- Horary, particularly out of Lilly: Regiomontanus, since that is what the rules were tested against.
- Hellenistic or traditional natal work: Whole Sign, since that is what those sources used.
- Medieval material: Alcabitius, for the same reason.
- Modern Western natal and psychological work: Placidus, which is what almost all the modern literature assumes.
- Charts near the poles: Whole Sign or Equal, because the time based systems fail there.
If you are learning, pick one and get fluent in it before comparing. Learning two at once tends to create escape hatches, where a placement that does not fit in one system gets quietly reassigned to the other. Once you can read a whole chart in one system, comparing becomes genuinely useful rather than a way to avoid a conclusion.
Frequently Asked Questions
Does Changing House Systems Change My Rising Sign?
No. The Ascendant degree and its sign are the same in every system. What changes is how the rest of the chart is divided from there.
Does Whole Sign Ignore The Midheaven?
No. The Midheaven remains a sensitive degree and is read for career and public life. It simply falls wherever it falls, often in the ninth or eleventh, rather than defining the tenth cusp.
Is Placidus Better Because It Is More Complicated?
Complication is not precision. Placidus divides time and Whole Sign divides the zodiac. Those are different design choices, not different levels of sophistication. Pick the system whose logic you can follow through an entire reading.
Why Do So Many Apps Default To Placidus?
Because printed Placidus tables were the ones most widely available in the nineteenth and twentieth centuries, so it became the convention, and software inherited the convention.
Recommended Reading
Book links below are Amazon affiliate links. As an Amazon Associate I earn from qualifying purchases, at no extra cost to you.
- Chris Brennan, Hellenistic Astrology (2017), on the twelve places and whole sign division.
- Demetra George and Chris Brennan, Ancient Astrology in Theory and Practice, on traditional method.
- Anthony Louis, Horary Astrology: The Theory and Practice of Finding Lost Objects, on Regiomontanus, its adoption, and Lilly's dependence on it.
- Dane Rudhyar, The Astrological Houses, for a modern interpretive approach.
Continue Learning
Next: What Do the 12 Houses Mean in Astrology? and How to Read a Birth Chart.