A poor person needs tzedekah. Can I donate an amount to him knowing that the money given to him will be through some tzedekah agency, from which i will receive a tax deductible receipt? I presume some of my donation will be given to the organization, but I am uncertain of the percentage.
In general, we are allowed to donate money to a tzedakah organization even though he will benefit from the tax-deductible receipt, because we are allowed to benefit from the tzedakah that we give. Therefore, if you just want to give a donation, you can do it through the tax-deductible organization even though they will deduct some of the money for themselves. If however you already told the person that you will give him a specific amount of money, and you know the organization will take off a percentage, then add to what you will give to the organization, so the poor person will receive what you said you will give.
Taz Y:D 249-1, Poskim