How letters become numbers
In the Pythagorean system the alphabet is numbered in order and repeats after nine, so A, J and S are all 1. The Chaldean system assigns values by sound instead of alphabetical order and never uses 9, which it treats as sacred. Results from the two systems usually differ, and that is expected rather than an error.
Each tool here shows the letter-by-letter working, so you can see exactly which letters carried the total rather than trusting a single figure.
Birth names, married names and chosen names
The convention is that the full birth name gives the core reading, while any name you have taken since gives a second, current-name reading that describes the energy you are living under now. Both can be true at once, and most people find the gap between them the interesting part.
The expression number and personality number are the two name-based readings people run most often.
Naming something new
Baby names, band names, trading names and domains all get run through numerology for the same reason: the decision is permanent and people want one more angle on it. The name analyzer scores a name and shows what is driving the score.
Use it as a tiebreaker rather than a rule. A name you dislike will not improve because it adds up to a favourable number.