Chara Dasha is entirely sign-based, not star-based like Vimshottari. "Chara" means "moving"; the sequence of dasha signs and their durations move and change based on two variables: the native's Lagna modality and where each sign's lord is placed.
K.N. Rao's method (most widely used):
If Lagna is Savya (odd-numbered, moveable: Aries 1, Gemini 3, Leo 5, Libra 7, Sagittarius 9, Aquarius 11), dashas proceed forward through the zodiac: Aries → Taurus → Gemini → ... If Lagna is Apasavya (even, fixed: Taurus 2, Cancer 4, Virgo 6, Scorpio 8, Capricorn 10, Pisces 12), dashas proceed backward: Taurus → Aries → Pisces → ...
Duration = count from dasha sign → dasha sign's lord (in the appropriate direction) minus 1 year. Example: Aries lord is Mars. If Mars is in Gemini, count Aries (1) → Taurus (2) → Gemini (3); duration = 3 - 1 = 2 years. If Mars is in Aries (own sign), duration = 12 years (standard rule).
This produces dasha periods that range from 1 to 12+ years, far more variable than Vimshottari's fixed cycles. Some years are short, others long, reflecting karmic intensity in that sign's domains.
Scorpio and Aquarius have dual lords (Mars+Ketu for Scorpio, Saturn+Rahu for Aquarius). The calculator uses the stronger of the two for duration calculation.
The engine computes Chara Dasha periods for the entire life. You will track dasha transitions and correlate them with major life events to test the system's accuracy on your own charts.