"Donors must give their contribution checks on or by December 31st to be included in the church’s 2012 written acknowledgement of their contributions.
If it comes in the offering on or after January 1st…even if the check was backdated for 2012 …it would not be included in their 2012 annual contribution letter.
However, if comes through the mail, all checks dated AND postmarked in 2012 would be deductible in 2012 even if you received it in 2013."