The charity is required to provide a 1098-C no later than 30 days after they sell the vehicle, it sounds like they made the sale on 05/26/2016. You should, however, enter the donation on your 2015 return, as that is when you donated the vehicle.
You should amend your 2015 return to add the donation if you wish to receive the deduction. You can use the steps below to amend and enter the vehicle.
To file an amended return:
1. Wait for your return to be accepted or rejected by the IRS
2. Log into your account, and at your tax timeline select your "2015
Tax Year"
3. Select to "Amend (Change) 2015 return" and
follow the directions
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You will enter your vehicle donation on Form 8283. Depending on how
much the organization sold your vehicle for(Or the cars fair market value),
you will fill out either section A or section B of Form 8283.
For donating your vehicle you will receive a Form 1098-C(Or
receipt) from the charitable organization that has the sale info on
it.
To enter your vehicle donation:
1. Select "Federal Taxes" at the top of the page
2. Select the "Deductions & Credits" sub-tab
3. Scroll down to "Charitable Donations" and select
"Show More"
4. Select "Start" next to "Donations to
Charity in 2016"
5. Continue to answer the questions in the interview accordingly
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Select this link for more information: Charitable
Donations
