Equal House System
greek: ἰσόμοιρος οἶκος (isomoiros oikos) · latin: domus aequales
Definition
The Equal House system divides the zodiac into twelve consecutive 30° arcs measured forward from the degree of the Ascendant, so the Ascendant degree is also the cusp of the first house, the same degree of the next sign is the cusp of the second house, and so on. The Midheaven floats independently of the 10th-house cusp and can fall anywhere from the 8th-house through 11th-house range depending on latitude, time-of-day, and time-of-year.
In Tradition
Across Hellenistic, traditional, and modern Western practice, the Equal House system is read as the simplest quadrant-free alternative to whole-sign houses: it keeps the Ascendant as the master organizing principle of the chart while preserving the symbolic 30°-per-house geometry. Holden identifies it as the first historical variation on the older Sign-House (whole-sign) system, and Hand emphasizes that Equal House cusps differ from whole-sign "places" in being house-beginnings rather than intensity-points within signs that begin at 0°.
In Practice
Practitioners use the Equal House system as a standard option in contemporary Western software alongside Placidus, Koch, Regiomontanus, Porphyry, and Whole Signs. Clare Martin uses Equal Houses throughout her *Mapping the Psyche* curriculum (CPA London lineage) specifically because it lets the MC-IC meridian be analyzed as a separate factor from the 10th-4th house axis. Ptolemy's specification in *Tetrabiblos* I that the first house begins 5° above the Ascendant and extends 25° below, with subsequent houses following at 30° intervals, is read by Holden as evidence that Ptolemy used Equal Houses rather than a trigonometric quadrant system. The system was promoted in the 20th-century British revival by Margaret Hone at the Faculty of Astrological Studies (1954-1969).
Historical Origin
Equal House technique is attested in Hellenistic-era astrology — Ptolemy's *Tetrabiblos* (c. 150 CE) is read by Holden as the principal early witness, with Equal House supplanting strict whole-sign reckoning in subsequent Greco-Roman practice. The system enjoyed a 20th-century British revival via Margaret Hone and the Faculty of Astrological Studies; Hand's *Whole Sign Houses* (2000) carefully distinguishes Equal House from whole-sign reckoning.
Etymology
Origin: Latin. Meaning: Equal houses.
Further Reading
- James H. Holden, A History of Horoscopic Astrology
- Robert Hand, Whole Sign Houses
- Clare Martin, Mapping the Psyche Vol 2