The amount you can deduct for charitable contributions generally is limited to 50% of your adjusted gross income. Your deduction may be further limited to 30% or 20% of your adjusted gross income, depending on the type of property you give and the type of organization you give it to. You have to itemize deductions on Schedule A in order to 'count' your charitable contribution.
Read more here: https://www.irs.gov/taxtopics/tc506.html
