Whole-sign vs Placidus: why house systems disagree

Ask two astrologers to compute the same chart and the planets will match to the arc-minute. Ask which house a planet falls in, and you might start a fight. The disagreement has a name: house systems. It is the one place where chart software genuinely differs, so it deserves an honest explanation.

What a house system actually decides

Your chart needs two kinds of lines. The planets sit at measurable positions around the zodiac. The houses are the twelve life territories drawn on top: career, home, partnerships, and so on. Where those twelve boundaries fall is a choice. The zodiac is observed. The houses are constructed.

Every system agrees on the two anchors: the ascendant (the eastern horizon, start of the 1st house) and the midheaven (the highest point the sun reached that day, start of the 10th in most systems). They disagree about everything between those anchors.

Whole-sign: the oldest and simplest

Whole-sign does one thing. Your rising sign becomes your 1st house, all of it, and every following sign is the next house. If you have Libra rising, all of Libra is your 1st house, all of Scorpio is your 2nd, and so on around the wheel.

This is the system of the oldest surviving horoscopes, and it never breaks. No latitude problems, no fallback rules at extreme birth places, no ambiguity about a planet two degrees from a boundary. A planet at 29° of a sign is in that sign's house, full stop. Its weakness is precision: everything in a sign shares one house, so house cusps are coarse.

Placidus: the modern default

Placidus divides the sky by time. Each house represents roughly two hours of the day's rotation, so cusps land at irregular degrees and houses have different sizes. The result tracks your exact birth time and place closely, which is one reason it became the 20th century default in most western software.

Its weakness is the edge case: in high latitudes the math can collapse, and software quietly falls back to another system for some houses. If you were born above roughly the Arctic Circle, check what your tool actually computed. Most people never hit this. The people who do deserve to be told.

What actually changes for you

• Your rising sign never changes. Houses are drawn after the ascendant is fixed.
• Planets comfortably inside a house usually stay put across systems.
• Planets near a cusp are where systems disagree. If a reading calls your Venus a 5th-house planet in one tool and 6th in another, that is a cusp case, not an error.
• Interpretations should say which system they used. A claim without that label is incomplete.

Our position, stated plainly

We default to whole-sign because it is unambiguous, it is what the historical record supports, and it never silently falls back. We compute Placidus alongside it because it is the modern default and comparing them is genuinely informative. Neither is a religion. The receipt panel always prints which one you are reading, and you can flip between them in the app. That is the whole stance: show both, label everything, let you decide.

If you want the foundations first, the birth chart guide explains what houses are for. To see your chart in both systems, cast it free.