Q: I’m calling about (the recent column on) Social Security disability benefits and their taxability. (The column shows the tax impact) if your total income exceeds a certain amount – $25,000 if you’re single, etc. Now, is that before deductions or after deductions? That’s very important and you should really state that when you’re talking about your income, whether that’s income before or after your Schedule A deductions

B.W., North Providence, R.I.

A: It’s neither. And that’s just one of the things that many readers find so confusing and frustrating about this issue.

To figure out whether at least some portion of your Social Security benefits will be subject to federal income tax, you must do a separate calculation.

You don’t do it on the Form 1040 itself. You don’t do it on Schedule A, or on any other such form, schedule or attachment. Instead, you do the calculation on a worksheet that’s published in your federal income-tax booklet.

So you don’t use any of the myriad rules normally associated with those forms and schedules. You don’t get into exemptions or deductions. Income means income (it even includes tax-exempt income!).

In other words, the normal rules – including the ones you cited in your question to MoneyLine – simply don’t apply.

(The worksheet for calculating tax on Social Security benefits is also available in various other Internal Revenue Service publications. You can also do the calculation by using special computer software, or on your own, with pencil and paper, if you know the rules well enough. Just bear in mind that it can be tricky.)

Neil Downing is a Providence Journal staff writer and author of “The New IRAs and How to Make Them Work for You.”