Placidus vs. Whole Sign vs. Equal: House Systems Explained

If you've ever noticed that your planets land in different houses depending on which astrology website you use, you've encountered one of astrology's oldest debates: which house system is "correct"?

The short answer is that there is no universally correct house system. Different systems make different mathematical choices about how to divide the sky, and each has strengths and weaknesses. Understanding why they differ helps you choose the one that works best for your practice.

What Houses Are

The twelve houses divide the sky (from the perspective of a specific location on Earth at a specific time) into twelve sectors, each representing a different area of life: self, resources, communication, home, creativity, health, relationships, transformation, philosophy, career, community, and the unconscious.

All house systems agree on the Ascendant (the eastern horizon) and the Midheaven (the highest point the ecliptic reaches). Where they disagree is how the space between these points gets divided.

Whole Sign Houses

How it works: The simplest system. Whatever sign is rising becomes the entire 1st house. The next sign is the entire 2nd house. And so on. Each house is exactly one sign, exactly 30 degrees.

History: This is the oldest house system, used by Hellenistic astrologers from roughly 100 BCE to 800 CE. It fell out of use in the medieval period but has been revived dramatically in the past 20 years.

Strengths: Clean, simple, unambiguous. Every planet in a given sign is in the same house, which makes interpretation straightforward. Works well at all latitudes, including extreme northern and southern locations where other systems break down.

Weaknesses: The Midheaven can float between the 9th and 11th houses rather than always marking the 10th house cusp. Some practitioners find this unsatisfying.

Best for: Traditional astrology, beginners who want clear house assignments, charts at extreme latitudes.

Equal Houses

How it works: Start at the Ascendant degree and add exactly 30 degrees for each house cusp. Like Whole Sign, each house is exactly 30 degrees, but the starting point is the Ascendant degree rather than the beginning of a sign.

History: Used alongside Whole Sign houses in the Hellenistic period, and remained popular through the medieval era, particularly in the British tradition.

Strengths: Simple to calculate, consistent house sizes, the Ascendant always begins the 1st house precisely.

Weaknesses: Like Whole Sign, the Midheaven doesn't necessarily mark the 10th house cusp. House cusps can fall in the middle of signs, which some find awkward.

Best for: Those who want simplicity but prefer the Ascendant degree as the starting point.

Placidus

How it works: Divides the sky based on the time it takes for each degree of the ecliptic to move from the horizon to the Midheaven. This creates houses of unequal size that vary based on the time and latitude of the chart.

History: Developed in the 17th century, it became the dominant system by the 20th century largely because the tables needed for calculation were widely published.

Strengths: The Midheaven always marks the 10th house cusp, which many astrologers find essential for career interpretation. The unequal house sizes feel intuitively "right" to many practitioners, as they reflect the actual astronomical geometry of the moment.

Weaknesses: Houses become extremely distorted at high latitudes (above about 60 degrees), with some houses becoming tiny and others enormous. The interception of signs (where an entire sign is contained within a single house) creates interpretive complications.

Best for: Modern psychological astrology, career analysis (MC always on 10th), tropical locations.

Which Should You Use?

There is no wrong answer, but here are some guidelines:

If you're interested in traditional astrology (Hellenistic or medieval techniques), use Whole Sign. The techniques were designed for it.

If you want the most popular modern system with wide support, use Placidus. Most websites, software, and textbooks default to it.

If you live at a high latitude (Scandinavia, Canada, etc.), consider Whole Sign or Equal, as Placidus can produce unusable charts.

The most practical advice: try reading your chart in multiple house systems and see which one produces interpretations that resonate most strongly with your actual life experience. The house system that helps you understand yourself better is the right one for you.