Whole-sign houses explained
Whole-sign houses is the simplest house system: each sign counted from the Lagna's sign is one full house.
What it is
In this system the house boundaries are the sign boundaries, so a planet at 29 degrees of a sign is in the same house as a planet at 0 degrees of that sign. It is the system used by most traditional Jyotish texts.
How it is worked out or read
Find the sign of the Lagna, call it house 1, then number the following signs 2 to 12. This site uses whole-sign houses for every chart and for the Manglik check. The Kaal Sarpa check uses the Rahu–Ketu axis, not houses.
Where it appears on this site
The birth chart uses this system. The method page states the formula.
A worked example
Take a Lagna in Simha. House 1 is Simha, house 2 is Kanya, house 3 is Tula, and so on until house 12, which is Karka. A planet at 28 degrees of Kanya falls in house 2, even though it is only two degrees from the boundary with Tula. A planet at 1 degree of Tula, two degrees beyond that boundary, falls in house 3. The rule is simple and does not depend on the exact degree of the Lagna. The cost of this simplicity is that a planet close to a sign boundary is placed by sign alone. That is the trade-off that the whole-sign system accepts, and it is one reason traditional texts relied on it.
Why many readers prefer it
Whole-sign houses are easy to check by hand, which is valuable for anyone learning to read a chart. Each house is a sign, so the reader never has to decide where a cusp falls. The system also keeps the sign and the house tied together, so that the qualities of a sign and the themes of its house can be read as one picture. Many modern systems draw cusps at computed degrees, which can split a sign between two houses. The whole-sign approach avoids that split, and this site uses it for every chart so that the result can be verified with pencil and the sign table.
Whole signs and the Lagna degree
Some readers worry that whole-sign houses ignore the exact degree of the Lagna. They do, by design. The Lagna degree still matters, because it determines the Lagna sign and the Moon's and other grahas' relations to it, but it does not move the house boundaries. A reader who wants to see the effect of the exact Lagna degree can compare with an equal-house chart, as the equal house article explains, and see which planets change house. The comparison is informative and shows the limits of either system.
Whole signs and the chart's simplicity
Whole-sign houses are simple because each house is a sign, and a reader can check every placement with a sign table. This simplicity is a practical virtue for learners and for anyone who wants to verify a chart by hand, and it is one reason the method is widely taught.