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House systems: why charts disagree
You compute a chart on two sites and get different houses for the same planet. Neither is wrong — they use different systems of division, and the difference is larger than is usually admitted.
Why there is a choice at all
Dividing the zodiac is easy: twelve arcs of thirty degrees, the same boundaries for everyone. Houses do not work that way. A house is a region of the daily rotation tied to a specific place on Earth, and that rotation is uneven against the zodiac: the Earth’s axis is tilted 23.4°, and the zodiac meets the horizon at an angle that depends on latitude.
So “divide the daily circle into twelve” has no single right answer. You can divide by degrees of zodiac, by time, by arc of ascension — and each method gives its own system.
The three most common
- Whole sign. The ascendant’s sign becomes the entire first house, the next sign the second. House boundaries coincide with sign boundaries. The oldest and simplest; it is what this site computes.
- Placidus. Divides not space but time: how long each point takes to rise from the horizon to the meridian. The most common in modern software.
- Koch. Similar to Placidus but measured from a different reference point. The difference between them is usually degrees, not signs.
Placidus and Koch are called quadrant systems: in them the ascendant starts the first house and the midheaven (MC) starts the tenth. By definition, always.
Here is the number the whole difference lives in
In whole sign the MC is not assigned anywhere — it falls where it falls. Here is where:
- house 84%
- house 946%
- house 1046%
- house 114%
6,528 charts sampled: latitudes from −55° to 60°, the whole year, every hour of the day. In quadrant systems the MC is the start of the tenth house always; in whole sign, about half the time.
Roughly half and half between the ninth and the tenth house. So for every second person the “top of the chart” in whole sign sits in the house of study and far places rather than the house of profession — while Placidus would have put it in the tenth without fail.
This is why the same planet in the same chart lands in the sixth house or the seventh. And it is why “which system is correct” has no answer: they answer slightly different questions.
Why we chose whole sign
Three reasons, and none of them is “it is more correct”.
- Its boundaries do not jump with the minute. In quadrant systems near high latitudes one house can stretch across two signs while its neighbour shrinks to a few degrees. An error in the birth time then costs considerably more.
- Beyond the polar circles quadrant systems break. Placidus is simply undefined there — some points of the zodiac never rise at all. Whole sign works everywhere.
- There is nowhere in it to hide an error. A house boundary coincides with a sign boundary, so the calculation can be checked by eye.
We are not claiming the others are worse. We are claiming that the choice was made and named — which is rarer than it sounds: most sites do not say which system they compute, and readers compare incompatible things without knowing it.
Where the argument came from
Whole sign is older: it was used in Hellenistic astrology of the first centuries, and it is the system the oldest surviving texts describe. Quadrant systems came later, along with a wish to tie houses not to signs but to the four angles — the horizon and the meridian.
Placidus is named after a seventeenth-century monk and mathematician, though the method was described before him. Its spread was mundane: in the nineteenth century printed tables appeared for that system, and it became the standard because it was the one at hand. Not because it won an argument — because it got printed.
Worth knowing for one reason: “standard” here does not mean “verified”. It means “convenient to typeset in 1890”.
At high latitudes it gets worse
Calgary is at 51 degrees, Kyiv at 50. At those latitudes quadrant houses are already noticeably uneven: one can stretch across sixty degrees while its neighbour shrinks to ten. A planet near a boundary then jumps between houses on a few minutes of birth time.
Beyond the polar circles Placidus breaks entirely — there are points of the zodiac that never rise or set, and “time taken to reach the meridian” does not exist for them. Programs either refuse to compute or quietly switch systems. The second is worse: the chart looks finished.
What to do about it in practice
If you see two sources disagree, the first thing to check is not “who got it wrong” but “which system”. A one-house discrepancy is almost always this.
And remember what the disagreement does not touch: the signs of the bodies, their degrees and every angle between them are identical in all systems. A house system changes only the answer to “in which area of life”, and nothing else. On the houses themselves, see the article on the twelve houses.
You can compute your own twelve houses in the chart form — in whole sign, and it says so right there rather than in small print at the bottom. If you are used to Placidus, some planets will sit one house further along than you expect; now you know why.