Porphyry House System Chart Calculator
Porphyry is the simplest quadrant house system: it takes your four angles (Ascendant, Midheaven, Descendant, IC) as already given, then splits the arc between each consecutive pair into three equal segments. No time arcs, no trigonometry, no great-circle projection, just arithmetic on angles already fixed.How it works ↓
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Porphyry is the simplest quadrant system: it takes the four angles (Ascendant, MC, Descendant, IC) and divides the space between each pair into three equal houses. No trigonometric time-arc math required.
Porphyry starts from your angles and does simple division, nothing more
Unlike Placidus, Koch, Campanus, or Regiomontanus, Porphyry doesn't calculate cusps from time arcs or great-circle projections at all. It takes the four angles your birth data already produces (Ascendant, Midheaven, Descendant, and IC) and divides the ecliptic arc between each consecutive pair of angles into three equal parts, giving you the three houses in each quadrant.
This makes Porphyry the most computationally simple of the quadrant systems: once you know the four angles, the other eight house cusps follow from basic arc division rather than any birthplace-dependent formula.
Porphyry is old, but simpler than Campanus or Regiomontanus
Porphyry is named for the 3rd-century philosopher Porphyry of Tyre and is one of the earliest quadrant systems on record, predating both Campanus and Regiomontanus by roughly a thousand years. Despite its age, it never developed the more elaborate geometric machinery those later systems introduced. It remained a straightforward equal division of the quadrant arcs throughout its history.
Reach for Porphyry when you want quadrant houses without the underlying complexity
Porphyry is a reasonable choice if you want houses that vary by quadrant like Placidus, Koch, Campanus, or Regiomontanus, but without relying on time-arc or great-circle calculations that can be harder to reason about or that behave unpredictably at extreme latitudes. It won't match Equal House's guaranteed uniform house sizes, but its cusp math stays simple everywhere the four angles themselves are computable.
How Porphyry compares to Placidus and Equal House
Placidus divides time along the celestial equator rather than dividing an arc evenly, so its intermediate cusps land at different points than Porphyry's even though both are quadrant systems built on the same four angles. Equal House, in contrast, ignores the angles between Ascendant and Midheaven entirely and just steps 30 degrees at a time from the Ascendant, so Equal House and Porphyry can diverge substantially, especially in quadrants where the angles aren't evenly spaced.
Against Campanus and Regiomontanus, Porphyry's plain arc-division approach is simpler than either system's great-circle projection, and will generally produce different intermediate cusps as a result.
Frequently Asked Questions
Does Porphyry change my Ascendant, Midheaven, Descendant, or IC?
No. Those four angles are inputs to Porphyry's calculation, not outputs, so they're identical to their values under Placidus or any other house system. Only the eight intermediate house cusps change.
Why would someone choose Porphyry over a more complex system like Placidus?
Mainly for simplicity and transparency, Porphyry's cusps follow from arithmetic on the angles alone, which some practitioners find easier to reason about than time-arc or great-circle methods, without the latitude-related failure modes those methods can hit.