DashaHQThe DashaHQ journal
How the dasha clock is computed, down to the arithmetic
Published 2026-09-29
This post is for the person who wants to check the app's homework. Every number below is classical Vimshottari mechanics, and every step can be reproduced with a calculator and one planetary position.
Step one: find the Moon's mansion
The sidereal zodiac runs from 0° to 360°, Aries through Pisces. Each nakshatra spans 13°20' (thirteen degrees twenty minutes, which is 360° divided by 27). Divide the Moon's sidereal longitude by 13°20' and the whole-number part of the result is the mansion index: Ashwini is 0, Bharani 1, Krittika 2, Rohini 3, and so on.
Step two: find the starting lord
The mansions map to planetary lords in a fixed sequence. Ashwini begins with Ketu, and the order runs Ketu, Venus, Sun, Moon, Mars, Rahu, Jupiter, Saturn, Mercury, then back to Ketu. Each lord owns three consecutive mansions, so the sequence wraps around the zodiac three times.
Step three: run the clock
The classical year-counts are fixed: Ketu 7, Venus 20, Sun 6, Moon 10, Mars 7, Rahu 18, Jupiter 16, Saturn 19, Mercury 17. The sum is 120 years, which is where the name Vimshottari comes from: hundred and twenty.
At birth you are partway through the starting lord's period. The fraction remaining comes from how far the Moon had traveled through its mansion: halfway through Ashwini means half of Ketu's seven years remained. From there the periods run in sequence, and when the list ends it wraps to the beginning for the next cycle.
Step four: nest the sub-periods
Each mahadasha divides into nine antardashas, one per lord, with lengths that stay proportional: the sub-period of lord X inside the period of lord Y lasts X's years times Y's years, divided by 120. Ketu inside Ketu runs 49/120 of a year; Venus inside Ketu runs 140/120. The same proportional rule generates pratyantardashas one level deeper. This part involves no approximations at all; it is exact ratio arithmetic.
How the software is checked
The engine is a port of a reference implementation, and a golden corpus of charts generated from that reference is part of the test suite. The corpus checks longitudes, the ascendant, the dasha chain, the works, to tight tolerances. When you read "Mercury mahadasha · Mercury antardasha" on the dashboard, that string sits at the end of a verified chain of arithmetic.
- Mansion = Moon longitude divided by 13°20'.
- Lords cycle in a fixed order with fixed year-counts summing to 120.
- Sub-periods are exact ratios. No approximations anywhere in the clock.
Curious what season your own chart is in? Start the 7-day trial — a daily reflection, computed from your birth data, for entertainment and self-reflection.