Line 21

If you are completing Part II-B and your employer withheld or you paid Additional Medicare Tax or tier 1 RRTA tax, use the Additional Medicare Tax and RRTA Tax Worksheet , later, to figure the amount to enter on line 21.

Withheld social security, Medicare, and Additional Medicare taxes should be shown on Form(s) W-2, boxes 4 and 6, and Puerto Rico Form(s) 499R-2/W-2PR, boxes 21 and 23.