> I make $100,000 this year, donate $20,000 to charity, pay taxes on $80,000 in income. Is this not accurate?
That sounds accurate.
> it can save you money if you're just over the bottom end of a tax bracket.
That sounds like a misunderstanding of tax brackets - if the brackets are (e.g) 20% up to $80k and 40% above that, with no deductions, what do you pay if you earn $80,001?