Calculating Compound Number

I assume by "compound" number you mean a number containing more than one digit.

What whole or parts of the name that need to be considered depends on what the number is for.

If the reading is for a personal numerology chart, then the full name — first, middle, last — is specified. If for a cornerstone reading, then only the first name is needed. If for an ancestral reading, then only the last name is needed. Those are examples. For a real reading, it generally is prudent to provide what is asked for.

How to Get the Best Numerology Reading has more information about that.

I don't know of any traditional numerology readings where the initial is used in lieu of a name.