Reading a dasha timeline

Vimshottari is the main timing system in Indian astrology. It divides a notional hundred and twenty years between the nine grahas in a fixed order, each getting a fixed span: Ketu 7 years, Venus 20, Sun 6, Moon 10, Mars 7, Rahu 18, Jupiter 16, Saturn 19, Mercury 17.

The order never changes and the lengths never change. The only thing your chart decides is where in the cycle you start — and that comes from how far the Moon had travelled through its nakshatra at the moment you were born.

Why the first period is a fraction

If you were born with the Moon a third of the way through a nakshatra ruled by Jupiter, you get the remaining two thirds of Jupiter's sixteen years — so about ten years and eight months — and then the sequence carries on in order.

This is why two people born on the same day at different times can be in different mahadashas for their whole lives.

The level that is actually useful

A major period of nineteen years is too coarse to plan around. Each one subdivides in the same proportions into antardashas, and those subdivide again into pratyantardashas.

The character of any stretch of time comes from the pair: the major period sets the subject, the sub-period sets the tone.

A common way to read a specific matter — career, say — is to find the lord of the house that governs it and look for that planet's sub-period inside the major period now running. That gives a window measured in months rather than decades. Looking only at that lord's own major period frequently lands somewhere useless: for a twenty-one-year-old with the Sun ruling the tenth house, it might not begin until 2070.

What a dasha is not

It is not a schedule of events. It is a claim that a particular planet's significations are prominent for a stretch, and that effort along those lines meets less resistance than it would otherwise. The dates are precise because the arithmetic is precise, not because the outcome is.