By PAULA SPAN

Are Social Security benefits taxable?

A recent post on young people’s attitudes toward Social Security drew this comment from a reader, rltlaw in Texas: “Let’s not forget that Social Security benefits are taxable as income.”

That’s not usually the case. Only 34 percent of beneficiaries pay federal income taxes on any of their Social Security income, the Social Security Administration says.

Here’s why: The taxability of benefits depends on your total income. As your income rises and passes certain thresholds, the proportion of Social Security benefits that becomes taxable increases as well.

The key factor is your “combined income,” defined as your taxable income (that’s the adjusted gross income on your 1040 federal tax return), plus any tax-exempt interest you receive, plus one-half of your Social Security benefits. (I’m relying, as usual, on The New Old Age’s own elder law attorney, Craig Reaves of Kansas City, to explain this stuff.) Whether none, or half, or 85 percent of your Social Security becomes taxable (you’re never taxed on 100 percent of it) depends on this number.