The Dwadashamsha chart, D-12, is the eighth of the sixteen divisional charts, formed by dividing each sign into twelve parts of two and a half degrees. It signifies parents and ancestry, the conditions of the father and mother, and what is inherited from the lineage. It is sometimes called the Suryamsha. An astrologer consults the D-12 for questions concerning the parents' health and fortunes and the ancestral inheritance, physical and karmic. The chart is one of the shodashavarga, the harmonic subdivisions through which jyotisha magnifies each department of a nativity. These are the interpretive conventions of the tradition; the divisional charts are a method for extracting focused readings from the single set of planetary longitudes recorded at the birth moment.
Unlike the parity-based Saptamsha and Dashamsha or the modality-based Navamsha, the Dwadashamsha uses the plainest possible rule: its twelve two-and-a-half-degree divisions are always counted forward from the sign itself, regardless of whether that sign is odd or even, movable, fixed or dual, so the first part of any sign stays in that sign and the twelfth part falls in the sign immediately before it, completing a full circuit of the zodiac. Because the rule never varies with the type of sign involved, the D-12 is one of the more straightforward of the sixteen to calculate by hand, and its consistency is sometimes cited as a reason ancestry and inheritance, matters understood as fixed by birth rather than shaped by circumstance, are assigned to it.