Astrolium ships 23 astrology house systems with whole-sign as the default, switchable in 1 click per chart. The active system is labelled in the chart legend, the PDF export metadata, and every text or JSON export. A reader with different software can always reproduce the chart from your output.
For the canonical Placidus-vs-whole-sign treatment with a how-to-choose decision tree, read the house systems guide. For the historical case for whole-sign as the default, see why we kept whole sign houses. For the related horary feature that defaults to Regiomontanus, see horary astrology. For the $29 per month Pro plan with all 23 systems, see pricing.
What a house system actually does
There are roughly 30 named house systems in the historical record, of which about a dozen are in active modern use. Astrolium ships 23, covering the full Western tradition and the closest Vedic equivalents.
Three reasons house systems matter. First: the same planet can fall in two different houses depending on the system, which changes the reading. A Mars at 28° Pisces in a Capricorn-rising chart sits in the 3rd house in whole-sign and the 2nd or 4th in Placidus, depending on the latitude. Different houses, different reads. Second: predictive techniques (profections, the time-lord chain) walk through the houses, so the system determines which year is what. Third: a chart published in one system is unreproducible to a reader using another unless the system is labelled.
The 23 systems Astrolium ships
The systems group into 4 families by their underlying geometry.
Sign-based (1)
Whole-sign. Each sign is one house. Cusps fall on sign boundaries. The Ascendant sign is the 1st house in full. Used by every Hellenistic astrologer whose work survives (Valens, Dorotheus, Ptolemy on most readings). Returned to mainstream Western practice through Project Hindsight in the 1990s. Astrolium's default.
Ecliptic-based (3)
Equal house. Each house is 30 degrees from the Ascendant; houses can split signs. The first house starts exactly at the Ascendant degree.
Vehlow. Equal-house but with the Ascendant placed at the centre of the 1st house (15 degrees in), not at the cusp. Common in some German traditions.
Porphyry. Trisects the quadrants. The simplest quadrant system. Documented by Porphyry of Tyre in the 3rd century CE and listed in some Hellenistic sources before that.
Time-based / quadrant (10)
Placidus. Divides the diurnal arc of each degree into 6 equal time portions. Dominant in 20th-century English-speaking practice. Fails above 66° latitude.
Koch. Divides the diurnal arc at the birth point. Popular in 20th-century German practice. Fails above 66° latitude.
Regiomontanus. Divides the celestial equator into 12 equal arcs and projects them onto the ecliptic. The medieval Latin standard before Placidus took over in the 17th century. The horary default for most working horary practitioners.
Campanus. Divides the prime vertical into 12 equal arcs. Geometrically the most elegant; rarely used in practice.
Alcabitius. Divides the Ascendant-to-MC arc into 3 time portions for each quadrant. The medieval Arabic standard, inherited by some Renaissance Latin authors.
Topocentric. A 20th-century refinement of Placidus, mathematically similar but computed differently. Used by some Argentine and Brazilian practitioners.
Krusinski-Pisa-Goelzer. A 21st-century system from three independent inventors that solves the high-latitude problem of Placidus while preserving its character.
Morinus. Projects equal arcs of the equator onto the ecliptic without quadrant constraints. A 17th-century system by Jean-Baptiste Morin.
Meridian (Axial). Divides the celestial equator into 12 equal arcs starting from the MC. Popular among uranian astrologers.
Horizontal. Projects equal arcs of the horizon onto the ecliptic. Geometrically aligned with the local horizon.
Hybrid / regional (9)
Sripati. Indian, the closest Western equivalent to the Vedic Bhāva Chalit. The cusps fall in the middle of the rasi house spans.
Sunshine. Places the Sun in the 9th house. A 20th-century European invention.
APC (Ascendant Parallel Circle). A 20th-century system tracking parallel circles to the Ascendant.
Pullen SD, Pullen SR, Carter, Bianchini, EQ-2, EQ-3. Six specialist systems for practitioners working within those specific lineages.
How to choose, in 5 questions
The choice of house system is a working astrologer's decision, not a software vendor's. Astrolium ships 23 because someone reading this paragraph needs exactly 1 of them.
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What tradition do you read in? Hellenistic, traditional, or Project Hindsight-influenced: whole-sign. 20th-century English-language sources or Western tropical mainstream: Placidus. German tradition: Koch. Medieval horary: Regiomontanus. Uranian: Meridian. Vedic-influenced Western: Sripati.
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What latitude are your clients at? Above 60° N or below 60° S, quadrant systems get unstable. Above 66°, Placidus and Koch fail entirely. Whole-sign, equal, or Porphyry work everywhere on Earth.
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What technique are you running? Predictive Hellenistic techniques (profections, zodiacal releasing) were developed for whole-sign and read most cleanly there. Primary directions were developed for Placidus and read most cleanly there. Horary is canonically Regiomontanus.
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Has the client been read in another system before? Once a client has a written reading in Placidus, switching to whole-sign mid-relationship breaks continuity. Astrolium lets you set the system per client, not just globally.
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What does the chart look like in each? When unsure, render the chart in 2 or 3 systems side by side. The system that produces a chart you can actually read is the right system for that chart. Astrolium's compare mode renders two wheels in 160 ms total.
The Placidus problem at high latitude
Robert Hand's writing on house systems is the canonical modern treatment of this issue. Placidus is built on the diurnal motion of the ecliptic, meaning the time it takes for a degree to rise from the horizon, culminate at the MC, and set on the western horizon. Above 66° latitude (the polar circle), some degrees of the ecliptic never rise or never set during certain weeks of the year. The diurnal arc becomes undefined and the house divisions cannot be computed.
This is not a numerical glitch. The mathematics genuinely break. Software that claims to compute Placidus above 66° is either using a fallback approximation or returning garbage. Astrolium flags any chart above 66° N or below 66° S with a warning and offers whole-sign, equal, or Porphyry as drop-in replacements with the same chart data.
Between 60° and 66°, Placidus and Koch still compute but produce houses that vary in size by a factor of 5 or more. A 50-degree first house against a 10-degree third house is technically correct but practically unreadable. Whole-sign keeps each house at 30 degrees regardless of latitude.
What the workspace looks like
Open settings. House systems. Pick your global default. Save. Every new chart you cast uses the chosen system. Override per chart by clicking the system label in the chart legend. The dropdown lists all 23, the chart re-renders in 80 ms, and the override is saved with the chart so the same client opens in the same system next time.
Compare mode opens two wheels side by side. Pick whole-sign in the left wheel and Placidus in the right. The cusps differ visibly. The planets stay at the same zodiacal degrees but fall in different houses where the cusps disagree. This is the most useful single tool for understanding what the choice of house system actually does.
Every export (PDF, PNG, JSON, text) names the active house system in the metadata. A reader downloading your chart in PDF and opening it in Solar Fire can recompute the cusps and confirm or challenge your work. The audit trail is complete by construction.
Versus what you have now
Most consumer apps: 4 house systems, hidden in settings, no label in the chart legend.
Solar Fire: 10 systems, named in the legend, switchable in 4 clicks.
Astro Gold: 12 systems, named in the legend, switchable in 4 clicks.
Astrolium: 23 systems, named in the legend by default, switchable in 1 click. Latitude warnings automatic. Per-client default supported. Compare mode renders 2 systems side by side in 160 ms.
Cross-link
For the in-depth Placidus vs whole-sign treatment with a decision tree, read the house systems guide. For the historical case for whole-sign as the default, see why we kept whole sign houses. For the related horary feature that defaults to Regiomontanus, see horary astrology. For the natal chart engine, see the natal chart feature. For the comparison against desktop software house pickers, see Solar Fire vs Astrolium.