What it means
Where the Mulank uses only the day, the Bhagyank sums the whole date — day, month and year — down to a single digit. Two people born on the same day of the month will usually have different Bhagyanks, which is what separates it from the Mulank.
How it is read
The conventional split is that the Mulank describes temperament and the Bhagyank describes the arc: the situations a life keeps returning to rather than the manner a person meets them in. When the two numbers agree, practitioners read the person as unusually consistent; when they conflict, as pulled between an instinct and a direction.
What to watch for
It uses the same digit-to-graha mapping as the Mulank and carries the same caveat: this is modern popular practice with a Chaldean and Pythagorean pedigree, not classical Jyotish, and no number is lucky or unlucky in itself.