Placidus vs Whole Sign Houses: Why Planets Can Change Houses

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You look up your chart on another site and your Sun is in the 9th house instead of the 10th, or your Moon has moved from the 1st to the 2nd. Very often the cause is not an error at all: one chart uses Placidus houses and the other uses Whole Sign houses. The planets sit at the same degrees in both. What differs is where the house lines are drawn.

This page puts one chart side by side in Placidus and Whole Sign houses, adds Equal houses from the Ascendant as a third column, and goes through each planet that changes house to show exactly why it moves. It ends with how to read a placement that has two possible house numbers.

Where the numbers come from. Astrologist.com calculates houses in Placidus, its default, or in Equal houses from the Ascendant when the birthplace is more than 66° north or south (exactly 66° stays Placidus). It has no Whole Sign option, no other house system and no house-system setting. On this page, the Placidus column comes from the same calculation code as the free birth chart. The Whole Sign and Equal columns are offline educational arithmetic, worked out from that chart's own planet positions and Ascendant; they are not Astrologist.com output. The Astrologist chat receives the house system and house placements of a chart calculated on the site, not comparison placements in other systems.

Two different rules

The two systems answer the question "which house is this planet in?" in different ways.

Whole Sign houses count signs. The rising sign is the 1st house, the next sign in zodiac order is the 2nd, and so on. To find a planet's house, count from the rising sign to the planet's sign. The degree inside the sign makes no difference. 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.

Placidus uses calculated cusps. The calculation produces twelve cusp degrees, and each house runs from its own cusp up to the next cusp: a degree exactly on a cusp belongs to the house that begins there, and a degree just short of the next cusp is still in the earlier house. Placidus cusps can fall anywhere inside a sign, so a sign can touch multiple houses, and one house can span parts of multiple signs, especially at higher latitudes.

Because of that, there is no reliable shortcut for predicting which planets move. The only dependable method is to compare each planet with the actual cusps, which is what the rest of this page does.

The worked chart: Ruben

Ruben is a fictional example used in several Astrologist.com guides. His chart is for London (51.5074° N, 0.1278° W) on 5 January 1993 at 12:00 local time, which in a London winter is also 12:00 UT. The time is treated as a recorded birth time. Tropical zodiac. The chart was recalculated with the routines that draw the free chart: Taurus rising, Ascendant 3°46' Taurus, Midheaven 13°46' Capricorn, Placidus houses.

The free chart does not print a cusp table, so the Placidus cusps below come from the calculation code, which returns them to 0.01°; they are shown with whole minutes cut off, as the free chart does for planets. The Whole Sign column simply lists the sign that makes up each house. The Equal column adds 30° steps to the Ascendant.

Notice that Gemini touches three Placidus houses (it holds the end of the 1st, the 2nd cusp and the 3rd cusp), while Libra holds no Placidus cusp at all and sits entirely inside the 6th house, an intercepted sign, with Aries intercepted opposite it in the 12th.

Here are the placements. Planet positions are the free chart's displayed values; the Nodes are the Mean Nodes the chart uses.

Seven of these thirteen bodies have a different house number in Placidus and in Whole Sign. That count belongs to this one chart only. It is not a typical rate: another chart can have fewer changes or more, depending on where its cusps fall.

Ruben's cases, one by one

Capricorn: the Sun, Uranus and Neptune move, Mercury does not. Capricorn is the ninth sign counted from Taurus, so in Whole Sign houses all four Capricorn bodies are in the 9th. In Placidus, Capricorn is split by the Midheaven at 13°46', which is the 10th cusp. Mercury at 4°25' Capricorn comes before that cusp and stays in the 9th. The Sun at 15°10', Uranus at 17°56' and Neptune at 18°31' come after it and are in the Placidus 10th.

Gemini: the Moon moves, the South Node does not. Gemini is the second sign from Taurus, so both Gemini bodies are in the Whole Sign 2nd. In Placidus, the 2nd cusp is at 6°30' Gemini. The Moon at 5°43' Gemini is 0°47' short of it, so in Placidus the Moon is still in the 1st. The South Node at 20°10' Gemini is past the 2nd cusp and before the 3rd cusp at 26°16' Gemini, so it is in the 2nd in both systems. The Moon is the only body in this chart that moves to a higher house number in Whole Sign; the others that change move to a lower one.

Cancer: Mars moves. Cancer is the Whole Sign 3rd. The Placidus 4th cusp, the IC, is at 13°46' Cancer, and Mars at 18°38' Cancer is past it, so Mars is in the Placidus 4th.

Leo: Chiron moves. Leo is the Whole Sign 4th. The Placidus 5th cusp is at 3°57' Leo, and Chiron at 22°48' Leo is well past it, so Chiron is in the Placidus 5th.

Aquarius: Saturn moves. Aquarius is the Whole Sign 10th. The Placidus 11th cusp is at 3°57' Aquarius, and Saturn at 16°49' Aquarius is past it, so Saturn is in the Placidus 11th.

The bodies that stay put. Jupiter in Libra is in the 6th in both, because the whole of Libra lies inside the Placidus 6th house. Pluto at 24°44' Scorpio is past the 7th cusp at 3°46' Scorpio, and Scorpio is the Whole Sign 7th. The North Node at 20°10' Sagittarius sits between the Placidus 8th and 9th cusps, and Sagittarius is the Whole Sign 8th. Venus at 1°39' Pisces is in the 11th in both, but for different reasons: in Whole Sign because Pisces is the eleventh sign from Taurus, in Placidus because it comes before the 12th cusp at 4°47' Pisces.

None of these cases follows from a simple rule about early or late degrees. Each one is settled by comparing the planet with the cusps that this chart actually has.

Equal houses: a third answer

Equal houses from 3°46' Taurus put a cusp at 3°46' of every sign. In Ruben's chart they agree with Whole Sign for every body except Venus. Venus at 1°39' Pisces comes before the Equal 11th cusp at 3°46' Pisces, so in Equal houses it is in the 10th, while both Placidus and Whole Sign put it in the 11th.

That one case shows why Equal and Whole Sign houses are separate systems even though both use 30° houses. Whole Sign houses start at 0° of each sign. Equal houses start at the Ascendant's degree in each sign, so any planet in the first 3°46' of a sign falls one house earlier in Ruben's Equal chart than in his Whole Sign chart. House systems explained sets out the three families side by side.

Ruben's Midheaven

In Placidus, the Midheaven at 13°46' Capricorn is the 10th cusp. In Whole Sign houses it is not a cusp at all: Capricorn is Ruben's 9th house, so his MC is a point inside the 9th. In Equal houses the 9th house runs from 3°46' Capricorn to 3°46' Aquarius, so the MC is inside the 9th there too. The Equal 10th cusp, 3°46' Aquarius, is a different degree from the MC.

That is Ruben's chart, checked by calculation. It is not a general rule about where the MC falls in these systems; in other charts it can sit in a different house. In both constructions the MC keeps its own meaning as a sensitive point. What is the Midheaven covers the point itself.

What else shifts with the houses

Empty houses. Counting all thirteen bodies in the table, Ruben's Placidus chart has the 3rd and 12th houses empty. In Whole Sign houses the 1st, 5th and 12th are empty, and in Equal houses the 1st, 5th, 11th and 12th. Empty houses explains how an empty house is read through its ruler.

House rulers. A house's ruler comes from the sign on its cusp, or in Whole Sign from the sign that is the house. Ruben's Placidus 10th cusp is in Capricorn, ruled by Saturn. His Whole Sign 10th house is Aquarius, ruled by Uranus, with Saturn as its traditional ruler. House rulers explained covers the method.

Overlays and transits. Any technique that drops a degree into the houses moves with the house system: another person's planets in synastry (house overlays and birth time) and transiting planets (transits through the houses) are placed by the cusps of whichever system you use.

What does not shift. Every planet's sign and degree, all the aspects, the Ascendant degree, the rising sign, the chart ruler and the MC degree are the same in all three columns.

How to read a planet that changes house

Take Ruben's Sun. It is a Capricorn Sun with the same aspects in every system. In Placidus it is in the 10th house, the area of public role, reputation and visible work. In Whole Sign houses it is in the 9th, the area of study, belief, travel and the search for meaning. An astrologer reading in Placidus might ask how Ruben's Capricorn sense of purpose tends to show up through his public role; one reading in Whole Sign might ask how it tends to show up through what he studies and believes. In both systems his Sun is about 1.4° from the MC degree, so its closeness to that angle is noted either way.

Neither reading makes the other chart wrong, and neither house is Ruben's "real" one. Each house system is a coherent method, and the difference is a shift in emphasis, not a change in the planet. Astrologist.com reads houses in Placidus, its default, and does not tell you which system to prefer.

Only with a reliable birth time

A comparison like this needs a reliable birth time. Ruben's Ascendant at 3°46' Taurus is close to the start of the sign: the same calculation gives an Aries Ascendant (29°39' Aries) at 11:52, so with a birth time just eight minutes earlier his rising sign would be Aries and every Whole Sign house in the table would change. The Placidus Moon is sensitive too: at 11:57 the 2nd cusp is still just behind the Moon, so the calculation puts the Moon in the 2nd house; by 11:58 the cusp has moved past it.

Whole Sign houses need only the rising sign, but the rising sign still depends on the time. Without a reliable time there are no natal houses in any system. A chart cast for noon, for sunrise or with the Sun placed on the Ascendant is a separate reference method, not a way to recover your natal houses; noon charts, sunrise charts and solar houses explains what each assumes.

To see your own Placidus houses, generate your free birth chart with an exact time. If another source disagrees with it, why your houses differ between charts is a step-by-step checklist. The methodology page sets out the site's house rules, and you can ask the Astrologist about the house placements in your chart.

Related articles

• House Systems in Astrology: Placidus, Whole Sign, Equal, Koch and More
• Why Your Houses Differ Between Astrology Sites: A Checklist
• How to Find Your House Cusps
• Intercepted Signs in Astrology
• What Is the Midheaven (MC)?
• Angular Planets