There are many different systems of Numerology. There's an African, an Arabic, and a Hebrew system of numbers. There's the Abracadabra system, which uses the pyramid technique. There's even a system of Japanese Numerology.
The Numerology systems commonly used here in the West are the Pythagorean and Chaldean methods. Of the two, the Pythagorean system is the more popular and easier to use. This explains why one numerologist may tell you your name or birth number is a 7, while another will say that you're a 3. The question to bear in mind is what system was used to arrive at your key number or numbers, and what do they mean?
Both the Pythagorean and Chaldean systems are similar in some respects, yet they have fundamental differences. On the similar side, both systems take your name and month, day, and year in which you were born into consideration. Both agree that people's names affect their character, and the birth date affects their destiny. Both systems are equally good in their own way at giving advice. Finally, numbers in both systems carry the same meaning, quality, character, and nature—this seems to be universal under all the systems.
For example, let's take an individual named VANCE LOUIS WHEELER, born August 3, 1975.
4+1+5 + 3 + 5= 18 1+8 = 9
3 + 6 + 3 + 9+1 =22
2 + 2 = 4
5 + 8 + 5 + 5 + 3 + 5 + 9 = 40 4 + 0 = 4
Total: 9 + 4 + 4 = 17 1+7 = 8
3 + 7 + 6+1+3 = 20
2 + 0 = 2
6 + 5 + 5 + 5 + 3 + 5 + 2 = 31
3 + 1=4
Total: 2 + 4 = 6