Placidus and Whole Sign divide the houses differently. With the same birth time, place and zodiac, a planet can change houses while keeping exactly the same zodiac position. Neither choice changes the astronomical instant of birth.
Use the house-system selector in the birth chart calculator to compare your own chart. This guide holds every other input fixed, so the comparison isolates the house system.
One birth, two house systems
Invented reference birth: June 15, 1990, 14:30, Singapore (UTC+08:00), latitude 1.2897°, longitude 103.8501°. The UTC instant is 1990-06-15 06:30 UTC. All positions use the tropical zodiac and apparent geocentric longitude.
Placidus
Whole Sign
| Point | Position in both charts | Placidus house | Whole Sign house |
|---|---|---|---|
| Sun | 23°55′ Gemini | 9 | 9 |
| Moon | 12°18′ Pisces | 5 | 6 |
| Mercury | 5°18′ Gemini | 8 | 9 |
| Venus | 18°30′ Taurus | 8 | 8 |
| Mars | 10°53′ Aries | 6 | 7 |
| Jupiter | 15°50′ Cancer | 10 | 10 |
| Saturn | 24°03′ Capricorn | 4 | 4 |
| Uranus | 8°10′ Capricorn | 3 | 4 |
| Neptune | 13°43′ Capricorn | 4 | 4 |
| Pluto | 15°24′ Scorpio | 1 | 2 |
| North Node | 9°42′ Aquarius | 4 | 5 |
| Black Moon Lilith | 24°52′ Scorpio | 2 | 2 |
In this example, the house assignments change for Moon, Mercury, Mars, Uranus, Pluto, North Node. The Moon moves from house 5 to house 6; its longitude does not move. The table includes the mean North Node and mean Black Moon Lilith as calculated points, separately from the ten solar-system bodies.
How the systems draw boundaries
Whole Sign starts house 1 at 0° of the Ascendant’s sign. Each following sign becomes the next house. The Ascendant remains a specific degree inside house 1. Placidus derives intermediate cusps from divisions of rising and setting time; its first cusp is the Ascendant and its tenth cusp is the Midheaven. House widths depend on latitude and sidereal time.
The Ascendant and Midheaven are 15°44′ Libra and 13°28′ Cancer in both charts. In Whole Sign, the MC does not have to be the start of house 10. Read why your Midheaven can be outside the tenth house for calculated examples.
Which system should you use?
Choose a convention deliberately and keep it consistent when following a book, teacher or interpretation. Agreement between a reading and your experience does not establish that one system predicts outcomes. Comparing systems can clarify which interpretive tradition a source uses; this calculation does not prove one tradition superior.
If an apparent discrepancy remains, follow the calculator comparison checklist. Match local time, historical time zone and tropical versus sidereal zodiac before comparing houses. A planet close to a cusp can also change houses with a small birth-time correction.
Method and limits
Both wheels use the same Astronomy Engine longitudes and local horizon calculation. The displayed degrees are rounded; house assignments use unrounded values. At latitudes where our Placidus solver cannot produce cusps, the calculator labels its Whole Sign fallback. No fallback occurs in this Singapore example. Without a known birth time, our tool omits houses rather than inventing them.
Download the unrounded comparison data (JSON). To reproduce it, run node scripts/build-comparison-research.ts from the project repository. The script uses the same calculation modules and saved station table as our tools. This is reproducibility within one implementation, not an independent accuracy check.
Cite this comparison
Natal Chart Lab (2026). Placidus vs Whole Sign Houses: Same Birth Chart Compared. Article and worked examples; supporting data. Calculated comparison output is available under CC BY 4.0: credit Natal Chart Lab, link to this article and the license, and indicate changes.
Prepared with AI assistance and checked against calculation code and saved examples. Astronomical calculations do not establish astrological claims about personality, relationships or future events.