IF you are using the software...you would put in the $$ exactly as shown on your 1099-INT form (1237.50 in box 8 and $500 in box 13). The software automatically reduces the 1099-INT box 8 value by the box 13 value before it puts in the line 2a value on the new 2018 form 1040. That's what the software is for...doing those calculations and putting the correct values in the proper places ..
_________________________
IF you are doing your tax return manually on paper...then yes, you would subtract 13 from box 8 before putting it on line 2a of the form 1040. but you have to add in any other 1099-INT's with box 8 values, or 1099-DIV forms with box 11 values into the line 2a value too.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
