Sadhya is the twenty-second nityayoga, and its name means that which can be accomplished, the attainable. It is one of the auspicious yogas, favourable for undertakings that require effort to bring to completion, promising that the goal is within reach. Reckoned from the summed longitude of Sun and Moon divided into twenty-seven parts, it advances as the lights separate through the month. In the panchanga it contributes its favourable, achievement-oriented quality to the reckoning of an auspicious time. These are the conventions of the calendar tradition, in which a benefic yoga such as Sadhya commends a moment for works meant to be carried through; the astronomical basis remains the simple arithmetic of the two luminaries' summed longitude over the lunar month.
Sadhya, that which can be accomplished, is grammatically a gerundive, a Sanskrit verbal form expressing what ought to or can be done, built from the same root, sadh, to accomplish or succeed, that gives Siddhi and Siddha their names; where those two describe a state already attained, Sadhya describes a goal still open and reachable through effort, a grammatical distinction that maps closely onto the difference in emphasis the tradition gives the three related yogas, attainment already achieved for Siddhi and Siddha, and attainment still to be worked for and genuinely possible for Sadhya.