This is a marriage reading, not a general compatibility percentage. It takes both partners' Mulank, Bhagyank, Naamank and Life Path and reads each pair as its own axis, with a reading written for what that axis is about in a marriage - daily temperament, the direction of a life, the names as they are used, and the Western Life Path. There is no combined score anywhere on the page, because nothing in this practice says how to weight one axis against another.
Reducing a couple to one number throws away most of what the practice actually reads. These four are kept separate because they answer different questions and can honestly disagree.
Numerology supplies a friend-or-not verdict for a pair of numbers. It does not supply cut-points, weights, or a rule for turning four verdicts into one figure. A percentage would therefore be an invention of whoever built the page, and it would look exactly as authoritative as one that was not.
What this page shows instead is a count - how many of the four axes came back as the same number or as mutual friends - printed beside the four rows it counts. It is a tally of facts on the page, not a measurement, and it is never converted into a percentage.
The 36-point Ashtakoot Guna Milan on the Kundli Matching page is computed from both partners' Moon nakshatras under named classical rules. This page is modern number practice with no classical Sanskrit source at all, and the page says so where the reading is made.
Averaging the two, or presenting a numerology figure as though it adjusted a guna total, would make the sourced reading unsourceable. So they are run separately and read side by side. Where they disagree, both stand - that is information about the couple, not an error in either method.
Entering a year adds each partner's Personal Year for it, with what that year is like to marry in. The two Personal Years are shown separately and are never combined: they are different quantities belonging to different people, and this practice has no rule for adding them.
For educational purposes. Astrological interpretations are traditional and not a substitute for professional advice.