Jyotiṣa timing method · deterministic chronology
Vimśottarī daśā: calculation, conventions, and limits
Vimśottarī daśā is a 120-year sequence used in Jyotiṣa. Maha Celestial calculates the chronology reproducibly; source-bound interpretation remains a separate layer.
Published 2026-08-18
Calculation chain
Moon longitude → Lahiri sidereal longitude → janma nakṣatra and elapsed fraction → remaining mahādaśā balance → nested subperiods.
The fixed 120-year order
The implemented sequence is Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn, and Mercury. Their conventional durations total 120 years. The sequence repeats; the natal Moon determines where the first reported period begins.
- Ketu 7 years
- Venus 20 years
- Sun 6 years
- Moon 10 years
- Mars 7 years
- Rahu 18 years
- Jupiter 16 years
- Saturn 19 years
- Mercury 17 years
How the opening balance is computed
The Moon’s Lahiri sidereal longitude identifies one of 27 equal nakṣatras. The untraversed fraction of that nakṣatra becomes the unexpired fraction of its ruler’s mahādaśā. Maha Celestial records the longitude, ayanāṁśa, boundary distance, year-length convention, and resulting timestamps so the timeline can be reproduced.
What can vary between implementations
Software can disagree because it uses a different ayanāṁśa, ephemeris, node convention, civil-time resolution, year length, or subperiod rounding policy. Those are calculation disagreements, not evidence that one interpretation predicts better. Maha exposes these choices instead of presenting a date without its method.
Interpretive boundary
A daśā date is a calculated result under declared conventions. It does not establish that the period causes or predicts an event.