Why is tax-exempt interest income on form 1040, line 2a added to total income?

[MichaelL1 · Accepted solution]

Line 2a is not added to Taxable income so it is not being taxed. 

It is income only not taxable income, and can make a difference on some other items on the return such as sales tax deduction or taxable amount of social security.

[ChiefRaven]

it is in mine also