Retirees whose only income is Social Security or railroad retirement benefits usually don't owe federal taxes. However, the IRS gets a cut when a retiree has other income from, for example, a post-retirement job or investment earnings. Married retirees who file joint returns also must take into account any money earned by either spouse in determining whether any of the federal retirement payments are taxable.
In most cases when a retiree's additional earnings are large enough to attract IRS attention, up to 50 percent of federal benefits generally are taxable. However, in some situations a retiree could find up to 85 percent of Social Security or Railroad Retirement benefits taxed.
Still, plenty of benefit recipients escape taxation. They are expected to account for almost $189 billion in taxes that the U.S. Treasury won't collect between 2011 and 2015.