Is box 12 d my contributions?

[rjs]

Box 12d on what form?

Contributions to what?

If you are referring to box 12d on a W-2, there is a one-letter or two-letter code before the amount. What is that code?

If it's a W-2 and D is the code, not the box number, then it is contributions to a 401(k).

[Opus 17]

Most W-2s have 4 places for information in box 12, they might be called "a", "b", "c" and "d".  Those letters are unimportant.  What counts is the one or 2-letter code in Capital letters.