The deduction, for those who qualify, is $6,000 per person. It's set to expire in 2028, at which point the percentage of seniors escaping this tax would presumably go back to around 64%.

The tax code is becoming charitable to many more donors thanks to changes in the new tax and spending law.

"The legislation that passed does make it so some people won't pay taxes on their benefits," says Marc Goldwein, senior vice president at the nonpartisan Committee for a Responsible Federal Budget.