Alain, In the US the full amount of one's contribution is deducted from income. That means that the amount that is deducted from one's taxes is dependent on one's either effective or marginal tax rate. Most Americans are in the middle effective tax rate which is 12.7 percent. The marginal tax rate for the middle income filers is about 22%. So if one is an average American tax payer, they would be able to deduct 22% of their contribution, more or less, from their Federal Income Tax.
Said simply, if I am a middle American and donated $100 to the WW&F, about $22 of that would be deducted from my Federal taxes. In Virginia, which has a 5.75% marginal income tax rate another $5.75 would be deducted from my State taxes.
If this is too confusing, please blame the Federal Government. It is outrageously complex because our government uses our tax system for social engineering and it is also influenced from the results from lobbying, which is favoritism.
Stay safe.
Bill