They say in order to be deductible for 2015, the contribution has to be made in 2015. When paying with a credit card, donations count for the current year, even if the bill isn’t paid until the new year. Also, checks count for 2015 as long as they’re mailed before the end of the year.
In order to be eligible for a tax deduction, donations must be made to a church, synagogue, temple, mosque, government agency, or another organization with a tax-exempt status. Donations must be recorded, and deductions need to be itemized on Form 1040 Schedule A.
For more information, visit the IRS online mini-course on charitable contributions.