The IRS doesn’t specify on its website, simply saying, “taxpayers who don’t itemize deductions may take a charitable deduction of up to $300.” I found at least one reputable source (the TaxAct blog) saying it’s $600 for married couples, but I believe they’re mistaken. In a footnote, the Joint Committee on Taxation’s description of the tax provisions of this law says, “The $300 limit applies to the tax-filing unit. Thus, for example, married taxpayers who file a joint return and do not elect to itemize deductions are allowed to deduct up to a total of $300 in qualified charitable contributions on the joint return.” That’s apparently going to be the rule unless there was further change in the legislation after the JCT prepared its description.
The deduction is entered on Form 1040 line 10b. The draft IRS instructions for that line say “Enter the total amount of your contributions on line 10b. Don’t enter more than $300.” Period. It doesn’t say anything about a different amount for a joint return.
Following up on my first reply, TaxAct has replied to my inquiry, confirming that the information in their blog was incorrect, and they have corrected that article to say the deduction limit is $300 regardless of filing status.