House systems: Placidus vs Whole Sign

What is a house, and why are there multiple systems?

Houses are the 12 areas of life in a birth chart: identity, money, communication, family, creativity, health, relationships, transformation, belief, career, community, and the unconscious. Which house a planet is in shows which area of life that energy concentrates in.

Here’s the catch: there is no single "correct" way to divide the sky-circle into 12 houses. Over centuries, different schools developed different mathematical methods. So the same chart can place a planet in the 9th instead of the 10th, depending on the system you choose.

Placidus: time-based and most common

Placidus is the most widely used system in modern Western astrology. It calculates house cusps by dividing the time it takes a point to travel from the horizon to the zenith. As a result, the houses are not equal in size; some are wide, others narrow.

Placidus emphasises the angular points (the Ascendant and the Midheaven/MC) and feels "accurate" to many people. However, at high latitudes (births near the poles) it breaks down mathematically; some houses stretch excessively or become undefined.

Whole Sign: oldest and simplest

The Whole Sign system is the oldest method of Hellenistic astrology and has made a strong comeback in recent years. Its rule is very simple: the entire sign of the Ascendant becomes the 1st house, the next sign the 2nd house, and so on. House = sign.

This simplicity is a big advantage: it works consistently at every latitude, there is no cusp ambiguity, and it’s clear which house a planet is in. The trade-off is that the MC is not always the start of the 10th house — the MC is read as a separate sensitive point.

Equal House in brief

A third common option is the Equal House system: starting from the Ascendant’s degree, every house is exactly 30°. It shares Whole Sign’s simplicity but keeps the Ascendant’s exact degree as the cusp. Think of it as a middle path between Placidus and Whole Sign.

Which should you choose?

Short answer: try both and see which describes your chart better. If you use traditional/Hellenistic techniques (zodiacal releasing, profections), Whole Sign is the natural choice. Modern psychological astrology and prediction techniques are mostly built on Placidus.

If you were born at a high latitude, Whole Sign may be safer. Most important is consistency: don’t switch systems mid-reading. Cosmir uses Placidus by default, because most modern users are familiar with it.