You can only deduct contributions of cash and property in
the year you actually make them.
You can’t claim 2016 contributions to charity on your tax
year 2017 return. To claim them, you’ll
need to amend your 2016 return.
For more information, see IRS Publication 526, Charitable
Contributions. (Note: This link is to the 2016 publication; the
2017 version hasn’t been published yet.)
https://ttlc.intuit.com/replies/3288565
