Regiomontanus House System Chart Calculator
Regiomontanus houses divide the celestial equator into twelve equal arcs, then project them onto the ecliptic through great circles. It was the standard Western house system for centuries before Placidus displaced it in the 20th century, and some practitioners still prefer it for horary and electional work today.How it works ↓
Calculating your placements…
Regiomontanus divides the celestial equator into twelve equal arcs and projects them onto the ecliptic through great circles. It was the standard house system in Western astrology for centuries before Placidus took over.
Regiomontanus divides the equator geometrically, not by time
Regiomontanus houses start by splitting the celestial equator into twelve equal 30-degree arcs, then project those arcs onto the ecliptic using great circles that pass through the north and south points of your horizon. That's a purely geometric division of the equator, distinct from Placidus, which divides the equator by time (how long a degree takes to rise) rather than by fixed arc length.
The result is a quadrant system, houses vary in size depending on birthplace latitude and time of birth, but with a different cusp calculation than Placidus, Koch, or Campanus.
Regiomontanus was the default for centuries before Placidus took over
Named for the 15th-century German astronomer Regiomontanus (Johannes Müller von Königsberg), this system was the standard house division used across Western astrology for roughly 200 years, from the Renaissance through the early modern period. Placidus, developed in the 17th century, only became the dominant default in general use during the 20th century, largely through its adoption by popular astrological software and reference tables.
Regiomontanus itself built on the earlier prime-vertical approach used by Campanus, applying similar great-circle projection to the celestial equator instead.
Reach for Regiomontanus for horary or electional astrology, or historical Western technique
Regiomontanus retains a specific following among horary and electional astrologers, who often prefer it over Placidus for those techniques specifically. It's also the natural choice if you're studying historical Western astrology from the Renaissance through the early modern period, when it was the prevailing standard.
How Regiomontanus compares to Placidus and Campanus
Regiomontanus and Campanus are the two oldest quadrant systems in this group and are frequently confused with each other, since both predate Placidus and both use great-circle projections, but Campanus projects from the prime vertical while Regiomontanus projects from the celestial equator, so their cusps differ even for identical birth data.
Against Placidus, Regiomontanus differs because Placidus's equatorial division is time-based rather than a fixed geometric arc, the two systems can produce noticeably different intermediate house cusps even though both divide the same equator.
Frequently Asked Questions
Is Regiomontanus still used today, or only historically?
Both. It's mostly known as a historical Western standard, but it has a genuine ongoing following among horary and electional astrologers who choose it deliberately over Placidus for those specific techniques.
Does Regiomontanus change my planetary aspects?
No, aspects are calculated from planetary positions and are identical across every house system. Only which house each planet falls into changes.