House Systems in Astrology: Placidus, Koch, Regiomontanus and Whole Sign
If you have run more than one report on this site, you may have noticed something odd. Your 3rd house sits in Cancer on the natal chart and in Leo on the Traditional report. Same birth date, same birth time, same city. Different houses.
Nothing is broken. Each report uses the house system its own tradition was built on, and this article explains what that means, why the four systems disagree, and how to set any report to the system you actually work in.
What a house system actually does
Your birth chart has two separate layers. The first is where the planets were, which is a matter of astronomy and is identical in every piece of software on earth. The second is where the twelve houses begin, which is a matter of geometry, and there is more than one defensible way to do it.
The problem is that the sky is a sphere and a chart is a flat circle. Dividing a sphere into twelve is not a single obvious operation. You can divide the ecliptic itself, or the celestial equator, or the daily arc each degree travels between rising and culminating, or the space around the observer. Each choice is internally consistent, and each produces different cusps.
Two things stay fixed across every quadrant system. Your Ascendant is your Ascendant, and your Midheaven is your Midheaven. Those come from the horizon and the meridian, and no house system moves them. What moves is everything in between.
The same chart in seven systems
Say Julian Hart was born in London on 8 January 1947 at 9:15 in the morning, at 51n30 and 0w07. Julian is an example rather than a real person, but the chart is real: you can reproduce every figure below on this site in under a minute. His Ascendant is 9°15' Aquarius, and it sits there in every quadrant system. Watch the 2nd cusp instead.
2nd, 3rd and 4th house cusps
Koch: 19°56' Pisces, 5°32' Taurus, 7°31' Gemini
Porphyry: 18°40' Pisces, 28°06' Aries, 7°31' Gemini
Placidus: 9°45' Aries, 15°27' Taurus, 7°31' Gemini
Regiomontanus: 11°44' Aries, 19°43' Taurus, 7°31' Gemini
Campanus: 2°20' Taurus, 26°53' Taurus, 7°31' Gemini
Whole Sign: 0°00' Pisces, 0°00' Aries, 0°00' Taurus
Equal: 9°15' Pisces, 9°15' Aries, 9°15' Taurus
Start with the 4th cusp. Koch, Porphyry, Placidus, Regiomontanus and Campanus all give 7°31' Gemini, to the arcsecond. That is the Imum Coeli, the point opposite the Midheaven, and every quadrant system anchors to it. The angles are fixed. The disagreement lives entirely between them.
Now the 2nd cusp, and this is the part worth sitting with. Koch puts it in Pisces, Placidus puts it in Aries, and Campanus puts it in Taurus. Three different signs, from one birth moment, all calculated correctly. There is no arithmetic error anywhere in that list.
The consequence shows up in the chart itself. Julian's Saturn is at 6°51' Leo, and the Placidus 7th cusp falls at 9°15' Leo. Saturn misses it by just over 2 degrees, so under Placidus it sits in the 6th house, the house of work and daily labour. Under Whole Sign, where the whole of Leo is the 7th, that same Saturn is a 7th house Saturn, and you would read it as a statement about partnership. Same planet, same degree, two different lives described.
One more thing worth noticing. London sits at 51.5 degrees north, and the spread above is wider than the same exercise produces near the equator. The further from the equator a birth happens, the more the quadrant systems disagree with each other. If you were born in the tropics, your cusps will look similar across most systems. If you were born in northern Europe or Canada, they will not.
The same chart, drawn three ways
Here is Julian's chart as this site draws it, in Placidus, in Koch, and in Whole Sign. The planets sit at identical degrees in all three. Only the house spokes move.
Notice how regular the Whole Sign wedges are. Every one is exactly 30 degrees wide. The two wheels above it divide the same circle unevenly.
What each report defaults to
The site offers eleven house systems, and the default is chosen per report to match the tradition that report works in. Here is the full map.
Placidus: the natal chart and most other reports
Whole Sign: Traditional, Time Lords, Zodiacal Releasing, Harmonics, Heliocentric
Regiomontanus: Horary, Electional, Events
Koch: Intelligence & Psychological Blueprint
Campanus: Western Sidereal, and also Solar Return and Lunar Return when you run them in sidereal
Every one of them can be changed. Solar Return and Lunar Return are the interesting case, because their default depends on the zodiac you pick. In tropical they open in Placidus, and switching them to sidereal moves them to Campanus so they match the sidereal natal report.
Placidus, on the natal chart
Placidus works from time. It takes the arc each degree of the ecliptic travels between rising and culminating, and splits that arc into thirds. It became the default in modern Western astrology partly through the accident of which tables were printed cheaply in the nineteenth century, and partly because it handles the middle latitudes where most of its users live perfectly well.
It has a hard limit, though, and you can watch it arrive. Because a degree of the ecliptic has to both rise and culminate for the method to work, Placidus becomes undefined once some degrees stop rising at all. That happens at the polar circle. Moving Julian's chart northward, the cusps compute normally at 66.5 degrees of latitude and fail at 66.6, which brackets the polar circle at 66°33'40". Koch breaks at exactly the same point for the same reason.
When that happens, this site switches the chart to Whole Sign and tells you so above the wheel. Whole Sign needs only the rising sign, so it works at any latitude, and it gives twelve equal houses of 30 degrees. The alternative would be Porphyry, which divides the arc between the angles into thirds and so never fails outright. We do not use it here, because that arc itself collapses near the pole: at Tromsø latitude Porphyry can produce one house of about 4 degrees sitting beside another of about 56, which makes a planet's house placement depend on a few arcminutes of birth time. Equal houses stay readable.
So a chart cast for Tromsø, Murmansk or anywhere else inside the Arctic or Antarctic Circle is drawn in Whole Sign. You can still switch it to anything you like using Change, including Porphyry, once you know why the default moved.
Koch, on the Intelligence & Psychological Blueprint
Koch is also a time-based system, calculated from the birthplace latitude, which is why it is sometimes called the birthplace system. This report follows the Huber method, and the Huber Age Point moves through the houses at a rate derived from Koch's own division of the quadrant. Run the Age Point on equal houses and every house becomes exactly 30 degrees wide, the progression becomes uniform, and the timing stops meaning what it says. Koch is not a preference here. It is load-bearing for the technique.
Regiomontanus, on Horary
Regiomontanus divides the celestial equator into twelve equal parts and projects those divisions onto the ecliptic. It was the working system of the Renaissance and it is what William Lilly used. The judgment rules of horary astrology, which govern how you read a question chart, were written by people looking at Regiomontanus cusps. Using anything else means applying rules to a chart they were not written for.
Whole Sign, on the Traditional report
Whole Sign is the oldest house division in Western astrology and the one Hellenistic astrologers used. The sign containing your Ascendant becomes the entire 1st house, the next sign is the entire 2nd, and so on. There are no fractional cusps at all. It has returned to wide use over the last two decades through the revival of Hellenistic technique, and it is now the default in most phone astrology apps, which is why so many people are surprised when a quadrant system shows them something different.
Campanus, on the Western Sidereal chart
Campanus divides the prime vertical, the great circle running east to west through the point directly overhead, into twelve equal parts and projects those onto the ecliptic. The division is purely geometric, built from the space around the observer. Western sidereal astrologers have generally preferred it for the clean geometry of how it cuts the sky, and the Western Sidereal report follows that convention.
So which one is correct
None of them, and all of them. That answer is unsatisfying, so here is the more useful version.
A house system is a convention for asking a question, and the question determines which convention answers it best. Horary judgment rules assume Regiomontanus because they were built on it. The Huber Age Point assumes Koch because its arithmetic depends on it. Hellenistic technique assumes Whole Sign because that is what its authors saw. Modern psychological astrology grew up on Placidus.
Astrologers who have tested this over decades tend to land on the same practical position. Use the system that belongs to the technique you are using, and if you are simply reading a natal chart, use the one whose results you have learned to read accurately. Consistency matters more than correctness here, because your interpretive skill is calibrated to whatever you have been looking at for years.
Every report tells you what it used
Every report on this site prints its settings directly beneath the birth data, at the top of the page. The natal chart shows the zodiac, the house system and the orb system, each with a Change button beside it. Reports that lock a setting to their tradition simply show fewer of them.
Open the same chart on the Intelligence & Psychological Blueprint and the house system reads Koch instead, because that report needs it.
Click Change and the full settings panel opens, where the zodiac, house system, node and Lilith variants and the orb system all sit together, with every orb standard spelled out beneath the selector.
If a chart here looks different from one you generated elsewhere, that line is the first place to look. Then change it. Click Change beside the house system and pick Placidus, Koch, Regiomontanus, Campanus, Whole Sign, Equal, Porphyrius, Alcabitus, Morinus, Topocentric or Vehlow, and the report regenerates around your choice.
Orbs move the same way
House systems decide where your planets live. Orbs decide which of them are talking to each other, and changing the orb setting can make an aspect appear or disappear entirely. The reports here use several different orb standards for the same reason they use different house systems, because each tradition set its own tolerances. That is a longer subject and it has its own article: Orb in Astrology: Permissible Deviation in Aspects.
If you have read this far and still want to know which system to actually use, we wrote a follow-up on how to choose your house system and orb system. It works through the decision using your birth latitude and a worked example.
You can generate any of these charts free at https://astrologyreadings.online.
