Numerology treats numbers as characters rather than quantities, and its procedure is fixed enough to describe exactly.
The Life Path comes from the birth date: the digits are added and reduced by repeated addition until a single figure remains, with 11, 22 and in some schools 33 held back as master numbers and left unreduced. The name yields further figures. In the system generally called Pythagorean, the letters A to I take the values 1 to 9, J to R repeat 1 to 9, and S to Z run 1 to 8. All the letters of a name give the Expression; the vowels give the Soul Urge; the consonants give the Personality.
Each digit then carries a settled character. One leads, two mediates, three communicates, four builds, five seeks change, six nurtures, seven withdraws and enquires, eight commands material affairs, nine completes and gives away. The practitioner combines the figures into a portrait, and derives personal year numbers from the current year for forecasting.
Two other systems are in use. Hebrew gematria assigns the values the Hebrew alphabet actually carries, from aleph at 1 to tav at 400, and is a genuine and very old feature of Jewish textual interpretation. Greek isopsephy does the same for the Greek alphabet. Both differ fundamentally from the modern method in that they operate on the alphabet's own numerals rather than on an assigned chart.
The point most worth noticing about the Pythagorean chart is that it fits the Latin alphabet and works in no other. The number it produces for a name is therefore a property of a modern spelling in a particular script, which is a constraint any account of the method has to accommodate.