Most people know that Social Security (SS) benefits are taxable. Still, many of us don’t fully understand how the tax rate on Social Security is applied. If SS represents your only income, it’s likely that your benefits aren’t taxable. However, if your monthly Social Security income is augmented by other taxable income, then 50 percent or 85 percent of your monthly benefit may be subject to federal income taxes (and possible taxation at the state level as well).