Can I claim donations made in a prior tax year?
No, you can only claim donations to qualified charitable organizations in the year they were made. When doing your 2016 tax return, you include donations made from January 1, 2016 through December 31, 2016.
If you didn't claim a donation to charity in a prior tax year, you could file an amended return. However, keep in mind that charitable donations only affect your return if you itemize deductions. Even then the donation amount may be limited, depending on what you donated and the type of charity.