Of Treasury Bonds? Or do you think other investment options are likely to do worse than 8.5% over the next 15 months?
Guaranteed 8.5% seems pretty good for the next 15 months. If I could put 20% of my portfolio into it, I'd be up for it. The big problem with it is that you are going to be subject to ordinary income tax when you cash it in or sell it. So if you keep it for 15 months, your after tax return is now 6.375% which is something like a 5.1% annual after tax return. Certain good for a guaranteed after tax return, but nothing earth shattering. The other problem is that with it being limited to 10k per person, it's just not going to move the needle that much unless you think we're going to be dealing with high inflation (and low returns on other assets) for a while and you're planning on putting $20k in a year ($10k per spouse) for a while.
ETA: Another thought: If you have a sub 3% mortgage, buying $10k per spouse of I-Bonds is maybe a good compromise for somebody that doesn't like having debt but also realizes that paying off mortgage debt at sub 3% doesn't make a lot of financial sense. Say you have a $400k mortgage at 2.75% interest. You put $20k a year in I-bonds and for the foreseeable future, you are going to be solidly beating your mortgage costs and also maintaining the liquidity (subject to a 12 month lockup for each purchase) to use the money for other purposes if needed. If the after tax return ever drops below your mortgage rate, then you can just cash in the I-bonds and put that amount toward the mortgage if you don't care about the liquidity or put it in an S&P Index fund if you still can't stomach paying down sub 3% debt. Over the long term, I'd probably still rather put that money in S&P funds (if that's not going to be inflation over the course of a 30 year mortgage, we have serious problems), but for the next couple of years at least, the I-Bonds would seem to offer a much better risk adjusted return.
