The Placidus House System is a method used in astrology to divide the natal chart into twelve houses. It is a quadrant house system, meaning the chart’s principal angles, including the Ascendant, Descendant, Midheaven, and Imum Coeli, help organize the house structure. The intermediate house cusps are calculated through divisions related to the apparent daily movement of points across the sky. Because the calculations depend on birth time and birth location, accurate birth information is especially important when using Placidus houses. Zodiacology’s Free Natal Chart uses the Placidus House System.