IRA question

You are correct, sir.

Correct, again. Roth contributions are never deductible. Instead, when you withdraw the money, the earnings are not taxed at all (provided you followed all the rules). The Roth also offers more flexibility because you can withdraw your contributions at any time.

As an aside, Roth eligibility is determined by your modified adjusted gross income (MAGI). This is not a really straightforward quantity to compute. However, your 401k deduction counts toward your MAGI. So if even if your gross income were $110,500, you could still qualify for a full Roth IRA contribution by contributing $15,500 to your (traditional) 401k. Then your MAGI would be at most $110,500 - $15,500 = $95,000.

--Bill

Probably. You are correct that you're subject to the income test for deducting traditional IRA contributions, but you don't use gross income for that test. You use Modified AGI, as explained in IRS Publication 590. The most important difference is that your 401(k) contribution reduces your gross pay when computing AGI.

Probably. Same comment about AGI applies. But your income other than wages/salary also adds to AGI.

The easiest way to wrap your head around the concept of AGI is to get a Form

If he's covered by a 401k, he cannot deduct traditional IRA contributions (correct?). So I would remove the "probably" and state he is correct, regardless of MAGI calculations. Cannot deduct because he is covered by a 401k.

It's a function of both, actually. A single filer who is not covered by an employer plan can always deduct a traditional IRA contribution regardless of MAGI. A single filer who is covered by an employer plan can still deduct a traditional IRA contribution if their MAGI is less than $50K (with a partial deduction allowed between $50K and $60K). Of course, the OP is not in this category.

The situation gets slightly more complicated if you're married and not covered by an employer plan. See IRS Pub 590, tables 1-2 and 1-3 for details.

--Bill