Deductions from one's income, for tzedakah

Hi,

We spend 10% of our income on tzedakah. Money spent for general taxes and sales taxes are not deductible from one's income before calculating the 10%, but money spent on income tax is deducted, because the amount that goes for income tax is viewed as though it had never been earned.

(Rav Moshe Feinstein, Igrot Moshe Yoreh Deah 1:143)

Have a great day,
Mordechai