21 out of 36

Eighteen out of 36 is the figure most often named as the pass mark, and a total of 21 clears it. That is worth saying plainly, because it is frequently not how the number arrives. Some people are handed it as a narrow escape. Others are handed it as a result to celebrate. Neither reading survives being placed against the rest of the population.

Clearing the mark is the ordinary outcome

There are exactly 108 nakshatra-pada positions, so every ordered pairing of one with another can be scored and counted — all 11,664 of them. Of those, 811 land exactly on 21, and 49.5% reach 21 or better. The mean across the whole population is 20.1.

That last figure is the one that rearranges the conversation. The pass mark sits below the score two arbitrary people would produce between them. Nothing has been selected for. No charts were matched. Take any two positions at random and the expected total is above the line that gets called a minimum.

A pass at 18 is not a bar cleared. 49.5% of all possible pairings reach 21 or better — no charts matched, nothing selected for.

What most commonly falls short at this total

A total hides its own composition. The 36 points are eight separate tests with very unequal weights, and two totals of 21 can be built from quite different pieces. What can be measured is which pieces are usually missing at this score.

Across the pairings that land on 21, the koota that most often scores nothing at all is Vashya, at 74.4% of them. It is one of the smaller tests, worth a fraction of the total, and what it compares is the classical grouping of the signs by nature — quadruped, human, water-dwelling, wild, insect — to say which of the two holds sway over the other. Its zero is common at almost every score on the board, including the very high ones, and most traditions attach no named dosha to it.

Next is Bhakoot, zero in 50.8% of pairings here. That one carries more weight. It compares the two moon signs by the count from one to the other, certain relative positions score nothing rather than part marks, and its zero is a named dosha that several traditions treat as material on its own. It is also the koota most often reported with a classical cancellation attached, which is a question about two specific charts rather than about a total.

Working the other way, the koota most often intact at 21 is Nadi, full in 91.1% of these pairings. The table below sets out the whole profile.

What can be checked from here

Three things about a total in this range are checkable rather than arguable.

Which tradition produced it. Several kootas are scored by more than one documented convention — the direction a tara count runs in, which graha maitri table is used, which varna table a source prints. Each is traceable to a named lineage, and a total can move by a point or two between them. Asking an astrologer to name the tables is a fair question, not a challenge.

Whether the birth times are right. The whole score depends on two nakshatra-pada positions. A birth time recorded to the nearest hour, or written down from memory years later, can put the moon in a neighbouring pada and change the total.

What the eight numbers say. A single figure was never the finding. The koota-by-koota breakdown is, and it is the same arithmetic for everyone who runs it.