The basic idea
The calculation connects a date to Major Arcana numbers. The result is often read as a personality card, a soul card, or a card pair.
Popular method
A common approach adds the digits in the birth date and reduces the result until it fits the Major Arcana range. Pair systems then connect that number to a related card.
Why methods differ
Some traditions reduce the month, day, and year separately. Others preserve higher Major Arcana numbers before reducing again. This is why two calculators can disagree without either one being malicious or broken.
Example calculation
1993-07-16 -> 1+9+9+3+0+7+1+6 = 36 -> 3+6 = 9
Which method should you use?
Use the method that matches the tarot tradition you are studying. If you are new, compare the methods and read the result as a reflective prompt rather than a fixed identity.