The correct form is “12th,” not “12nd.” This follows the typical rule for ordinal numbers in English, where numbers ending in “2” (like 2, 12, 22) use “nd” in their written form (e.g., “2nd”), but the 12th is the exception. Thus, you say and write “12th” for things like the 12th of January, or the 12th day of the month.
