Short answer: You’re getting robbed, and the system is bankrupt.
None, some or most of the payout you get from Social Security will show up on line 20b of your federal tax return and get taxed.
There’s a formula that spells out the dollar amount. Here it is, for joint returns:
Taxable amount = MIN(0.85*BENEFIT, 0.5*MIN(12000, BENEFIT, MAX(0, 0.5*BENEFIT + OTHER – 32000)) + 0.85*MAX(0, 0.5*BENEFIT + OTHER – 44000))
In this formula, BENEFIT is the year’s payout and OTHER is, to oversimplify a bit, your adjusted gross income from sources other than Social Security.