The overall ceiling on the deduction is 50% of adjusted gross income (AGI). Gifts of cash and short-term capital gain property to “public” charities are deductible up to this 50% limit. See IRC section 170(b)(1)(A).
Gifts to “public” charities of appreciated stock held long-term (together with certain other types of other long-term appreciated property contributions) are generally deductible up to 30% of AGI. See IRC section 170(b)(1)(C).
“Excess” contributions may be carried forward for up to five subsequent tax years. See IRC section 170(d)(1).