House systems compared

A house system divides the sky around a birth place and time into twelve areas called houses. Each area is linked with themes used to read a chart, such as relationships, work, home or shared resources. The system sets the boundaries, or cusps, between those areas. It does not change the zodiac positions of the planets; it changes which house a planet occupies and how the chart is arranged. Astrology uses these placements as a symbolic language for reflection, not as proof or prediction.

Placidus finds house cusps by dividing the time a degree of the zodiac takes to rise toward the Midheaven. Since that timing varies across the sky, the houses are unequal in size. The Ascendant and Midheaven remain important chart angles in this system, and their positions anchor the house layout. Placidus is the calculator’s default system where it can be defined. Near and beyond the polar circles, from about 67 degrees north or south, it is not defined; the calculator uses Porphyry there and identifies that choice.

In Whole Sign, the sign containing the Ascendant becomes the whole first house. The next sign becomes the second house, and the sequence continues around the chart. Each house therefore covers one full sign, while the Ascendant degree can fall somewhere inside the first house rather than marking its cusp. This makes the layout easy to follow by sign. The Midheaven can also fall in a house other than the tenth, so its placement does not necessarily match the house convention used by other systems.

Equal houses begin at the exact degree of the Ascendant. Each following house spans 30 degrees, so every house has the same width, but the sign boundaries do not necessarily line up with the cusps. The Ascendant degree is the first-house cusp; the Midheaven may land in a different house from the tenth. This method keeps the Ascendant as the starting point and gives a regular structure, while still allowing planets near a cusp to be assigned differently than they are in other systems.

Porphyry starts with the four angles: the Ascendant, Imum Coeli, Descendant and Midheaven. It splits each quadrant between adjacent angles into three equal parts to form house cusps. The resulting houses can be unequal, because the four quadrants themselves are not necessarily equal in size. The Ascendant and Midheaven are shared angle points with Placidus, though the intermediate cusps are calculated differently. Porphyry also provides the house layout this calculator uses when Placidus cannot be worked out near the polar circles.

The systems agree on some chart anchors and differ on others. Placidus and Porphyry share the Ascendant and Midheaven; Equal starts from the exact Ascendant degree. Whole Sign uses the Ascendant’s sign as the whole first house. Their other cusps can differ, which can place a planet in a different house. The calculator’s printed table shows one example chart in all four systems; its values depend on that chart’s birth details, so they are not general rules.

To compare them, use the same birth details and notice which house placements stay steady and which change. If the birth time is uncertain, house cusps and angles may also be uncertain, so a close comparison needs caution. This calculator needs a birth date and place, with birth time optional. It uses the tropical zodiac and supports years from 1900 to 2100. It offers Placidus, Whole Sign, Equal and Porphyry. Treat the system as a way to frame reflection, and choose the layout that is clearest to work with.