House Systems in Astrology: Placidus, Whole Sign, Equal, Koch and More

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A timed birth chart can be divided into twelve houses, but there is more than one way to draw them. A house system is the rule that decides where each of the twelve houses begins. Give two house systems the same birth data and the same zodiac, and the planets stay exactly where they are, yet the house lines can fall in different places, so a planet can end up with a different house number. That is the usual reason two charts for the same person disagree about houses.

This page explains what a house system does, the three families of house systems (Whole Sign, Equal and quadrant systems), the named systems in each, and which parts of a chart stay fixed when only the house system changes. It is a reference page; it does not rank the systems.

What Astrologist.com calculates. The free birth chart uses Placidus houses by default. For a birthplace more than 66° north or south of the equator it uses Equal houses from the Ascendant instead and says so on the chart; a latitude of exactly 66° stays Placidus. Those are the only two house systems the site calculates. There is no Whole Sign, Koch, Porphyry, Regiomontanus, Campanus or Alcabitius calculation and no setting for choosing a house system. The other systems on this page are described so you can recognise them elsewhere. The Astrologist chat is given your chart's house system and the house placements that chart produced; it does not calculate houses in any other system.

What a house system does

Signs and houses come from two different measurements. The zodiac signs are twelve 30° sections of the ecliptic, counted from the vernal point, and at any given moment they are the same for everyone on Earth. The houses describe the sky as seen from one place at one moment: which part of the zodiac is rising in the east, which part is culminating on the local meridian, which part is setting and which part is below the horizon. That is why houses need a birth time and a birthplace while signs, for most planets, need only a date.

A house system is the method that turns that local sky into twelve cusps, the zodiac degrees where the houses begin. Each house then runs from its own cusp up to the next one.

Signs and houses stay separate layers in the reading. The sign describes the style in which a planet tends to express itself; the house describes the area of life where that expression tends to show up. Changing the house system can change the second layer. It never changes the first.

The systems on this page all start from the eastern horizon in some way, through the Ascendant: the degree of the zodiac rising in the east at the moment of birth. They differ in how they get from there to the other eleven houses.

Whole Sign houses

In Whole Sign houses, each house is exactly one sign. The sign that contains the Ascendant, your rising sign, is the whole 1st house, from 0° to the end of that sign. The next sign in zodiac order is the 2nd house, the sign after that the 3rd, and so on round the circle.

Two consequences follow:

• The Ascendant degree is a point inside the 1st house, not its starting line. With 3°46' Taurus rising, the Ascendant sits near the start of the Taurus house; with 27° Taurus rising, it sits near the end. The 1st house is the whole of Taurus in both cases.
• A planet's house depends only on its sign. Count signs forward from the rising sign: a planet in the rising sign is in the 1st, a planet in the next sign is in the 2nd, and so on.

In Whole Sign houses, your rising sign occupies your 1st house; that is a feature of that chart construction, not a rule that a sign belongs to a house. Someone with Leo rising has Leo as their 1st house and Virgo as their 2nd; someone with Capricorn rising has Capricorn as their 1st house. The system ties houses to signs only inside one chart, through that chart's rising sign.

Historically, Whole Sign houses are attested in Hellenistic astrology, the Greek-language astrology of the last centuries BCE and the first centuries CE. That age is a fact about history; it is not evidence that the method is more correct than later ones.

Equal houses from the Ascendant

Equal houses also give every house 30°, but they count from the Ascendant degree rather than from the start of the rising sign. The Ascendant is the 1st cusp, the 2nd cusp is 30° further along the zodiac, the 3rd is 60° further, and so on. With an Ascendant of 3°46' Taurus, every cusp falls at 3°46' of a sign: 3°46' Gemini for the 2nd, 3°46' Cancer for the 3rd, 3°46' Scorpio for the 7th.

Whole Sign and Equal houses are easy to mix up because both use 30° houses. The difference is where each 30° block starts. Whole Sign houses start at 0° of a sign, so every house is one complete sign. Equal houses start at the Ascendant's degree within each sign, so most Equal houses contain the end of one sign and the beginning of the next. A planet placed earlier in its sign than the Ascendant's degree falls one house earlier in Equal than in Whole Sign. Placidus vs Whole Sign houses shows one case of that, with Venus.

Equal houses from the Ascendant are what Astrologist.com uses above 66° latitude. Chart angles at high latitudes explains how the site builds them, with worked cusps.

Quadrant house systems

Quadrant systems fix four cusps on the angles of the chart: the Ascendant is the 1st cusp, the IC the 4th, the Descendant the 7th and the Midheaven (MC) the 10th. Each of the four quadrants between those angles is then split into three houses, and the systems differ in how they make that split. Because the angles are rarely exactly 90° apart in zodiac longitude, quadrant houses are usually unequal in size, and the same sign can touch two cusps or none.

Placidus is named after Placidus de Titis, a 17th-century Italian monk and astrologer. It divides time: roughly, the time each degree of the zodiac takes to travel between the horizon and the meridian is split into thirds. It is the site default. Why Placidus houses differ in size sets out the mechanism and shows computed widths, so it is not repeated here.

Five other quadrant systems, described briefly. Astrologist.com does not calculate any of them, and no cusp values are given for them here.

• Porphyry. Each quadrant between the angles is divided into three equal parts measured along the zodiac. Once the angles are known, the rest is plain division.
• Koch. Named after the German astrologer Walter Koch (1895 to 1970), it is a 20th-century system. Like Placidus it works with time, but its intermediate cusps come from dividing into thirds the time the Midheaven degree takes to travel from the horizon up to the meridian.
• Regiomontanus. Named after the 15th-century astronomer Johannes Müller, known as Regiomontanus. It divides the celestial equator into twelve equal sections and carries those divisions onto the zodiac.
• Campanus. Named after the 13th-century scholar Campanus of Novara. It divides the prime vertical, the great circle that runs from the east point of the horizon through the point directly overhead to the west point, into twelve equal sections and carries those onto the zodiac.
• Alcabitius. Named after a 10th-century Arabic astrologer known in Latin as Alcabitius. It also divides time arcs into thirds, but it uses the arcs of the Ascendant degree for every intermediate cusp rather than a separate arc for each cusp.

Other house systems also exist. The descriptions above are deliberately short: each system has its own geometry, and the point here is recognition, not calculation.

High latitudes

Quadrant systems depend on how the degrees of the zodiac rise and set at the birthplace. Far from the equator some degrees rise very quickly, and inside the polar circles some never rise or never set at all. Some quadrant systems can therefore become undefined or impractical at high latitudes, and different systems run into trouble in different ways.

Astrologist.com handles this with one explicit rule rather than a quiet switch: above 66° north or south it uses Equal houses from the Ascendant, and exactly 66° remains Placidus. That 66° line is the site's own product rule. It is not the polar circle, which lies at about 66.5°.

Whole Sign and Equal houses can still be drawn at high latitudes because they need only the Ascendant, but they inherit any problem with it. Near the poles the Ascendant can move through several signs in a few minutes, and the site discloses a separate caution: in some polar cases its current Ascendant routine can return the western horizon intersection instead of the eastern one. A polar Rising sign, and every Equal cusp built from it, may therefore need independent verification. The details are on chart angles at high latitudes.

The Midheaven is not always the 10th cusp

In quadrant systems the MC is the 10th cusp by construction. In Whole Sign and Equal houses it is not. The true Midheaven stays a sensitive point in its own right, calculated from the moment and the birthplace, and it falls inside a house rather than on a house line. Which house that is varies from chart to chart. Its sign and degree do not change with the house system; only the house that contains it does.

On Astrologist.com's Equal-house charts above 66°, the wheel's "MC" and "IC" labels sit on the Equal 10th and 4th cusps, which are not the true MC and IC. That is a known, disclosed limitation of the fallback charts, explained on the high-latitude page.

What stays the same and what can change

With the same birth data and the same zodiac, switching only the house system leaves these unchanged:

• every planet's sign and degree;
• the aspects between planets;
• the Ascendant degree and the rising sign, and with them the chart ruler;
• the true Midheaven degree.

These can change:

• the house cusps;
• the house each planet sits in, including which planets fall in the angular houses;
• house rulers, because a house's ruler comes from the sign on its cusp, or the sign that is the house in Whole Sign, under the system in use (house rulers explained);
• intercepted signs and the same sign on two house cusps, which arise in unequal systems and never in Equal or Whole Sign houses;
• which houses are empty;
• whether the MC coincides with the 10th cusp.

Reading a placement that changes house

When a planet changes house between systems, nothing about the planet itself has changed: same sign, same degree, same aspects. What shifts is the area of life the house layer points to. Astrologers who look at more than one system often treat both house themes as possibilities worth considering, rather than declaring one of them the true placement and the other a mistake. Placidus vs Whole Sign houses works through one chart to show what that looks like, and why your houses differ between charts is a checklist for when another site shows different houses from yours.

No house system works without a birth time. Whole Sign houses need only the rising sign, not the exact Ascendant degree, but the rising sign itself depends on a reliable time, and it can change within minutes. Without one, no system gives natal houses; how accurate your birth time needs to be explains how to test a time window.

To see your own houses, generate your free birth chart with an exact birth time; the line under the wheel names the house system used. The methodology page lists the site's calculation choices, and you can ask the Astrologist what a house placement in your chart could mean.

Related articles

• Placidus vs Whole Sign Houses: Why Planets Can Change Houses
• Why Your Houses Differ Between Astrology Sites: A Checklist
• Astrology Houses Overview
• Why Placidus Houses Differ in Size
• Chart Angles at High Latitudes
• House Rulers in Astrology
• How to Find Your House Cusps