So I poked around in the IRS forms a big (publication 1212 in particular). Looks like principal reductions can be used to offset the TIPS 1099 interest at least. What isn't clear is if a deflation-driven yearly principal reduction can apply to interest income from other things the invest holds. I'm betting the answer is no, but cannot find anything clear about it onlinefnord123 wrote:If the principal goes down (due to deflation) does that act as an offset to other income earned during the same year? I.e. if someone earned $50K in income, but their tips went down $5K in principal, would they then report $45K AGI on their year-end taxes?

Yeesh, ok, 2nd answer to my own questions - from form 1212:
From reading this gobbledygook, it seems like for a held-to-maturity TIPS bond, one would actually be no more tax-disadvantaged than one would be with a regular treasury held to maturity. If the net inflation was positive for the TIPS bond when held to maturity, one would realize the "phantom" income as real income when selling the bond. If the net inflation was negative for the TIPS bond when held to maturity, one would get to deduct the negative OID years as losses, essentially causing phantom income to go to zero in terms of tax payments over the long run, and would get the face value of the TIPS bond back at the end anyway.Net negative adjustment. A net negative adjustment exists for a tax year when the total of any negative adjustments described in (2) above for the
tax year is more than the total of any positive adjustments for the tax year. Use a net negative adjustment to offset OID on the debt instrument for the tax year. If the net negative adjustment is more than the OID on the debt instrument for the tax year, you can claim the difference as an ordinary loss. However, the amount you can claim as an ordinary loss is limited to the OID on the debt instrument you included in income in prior tax years. You must carry forward any net negative adjustment that is more than the total OID for the tax year and prior tax years and treat it as a negative adjustment in the next tax year.
The above matches the sentiment I've seen on TIPS over at Bogleheads, where several posts seemed to say that over the long run TIPS are no better or worse than regular treasuries in terms of tax treatment.
I am not a lawyer or accountant, so I could be completely wrong. Hopefully if I am someone will point out where
