Two dates of birth
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Your life path
Your partner's life path
How the rating is worked out
Each date is reduced to its life path by the site's method (day, month and year reduced separately, then added). The pair is then looked up in the tradition's table of temperaments. Numbers that share a rhythm (3 and 5, 2 and 6, 4 and 8) rate as natural matches. Numbers that pull against each other (1 and 8, 4 and 5, 6 and 7) rate as demanding, and the rest as workable. Master numbers are read on their base.
The table is published in full on the compatibility guide, so nothing here is hidden.
Questions people ask
Does a demanding rating mean we should not be together?
No. The tradition rates pairs by how easily two temperaments fit, not by whether a relationship works. Plenty of long marriages are between numbers the tradition calls demanding; the pair page says where the friction usually is, which is more useful than the label.
Why does the calculator use life path numbers and not names?
Because the life path is the number numerologists read as temperament, and temperament is what compatibility is about. Name numbers (expression, soul urge, personality) describe how you present and what you want, and the pair pages mention them where they matter.
What if one of us has a master number?
The tradition reads 11, 22 and 33 as their base numbers 2, 4 and 6 for compatibility, with a note that the master-number partner tends to feel things more strongly. The result shows both the master and the base.