我来科普 off the top of my head： 30 year tax deferred, could be tax free (with income limit) if used for education purpose etc and there is no credit risk. buy from treasury direct, limit 10K per SSN per year. Another 5K per year can be converted from your tax refund. interest payments contains two parts, fixed and float. fixed rate is set at the time of purchase and float gets reset every 6 month when CPI is released you have to hold onto i-bond for at least 12 months （almost) before you can redeem it for cash. If you redeem before 5 year is up, you forfait the last 3 month of interest If you buy last day of the month, you get the whole months of interest; if you sell after the first day of the month you retain that whole month's interest. you can have co-owners and beneficiaries and when you redeem you can designate which SSN will pay the tax.
30 year tax deferred, could be tax free (with income limit) if used for education purpose etc and there is no credit risk. buy from treasury direct, limit 10K per SSN per year. Another 5K per year can be converted from your tax refund. interest payments contains two parts, fixed and float. fixed rate is set at the time of purchase and float gets reset every 6 month when CPI is released you have to hold onto i-bond for at least 12 months （almost) before you can redeem it for cash. If you redeem before 5 year is up, you forfait the last 3 month of interest If you buy last day of the month, you get the whole months of interest; if you sell after the first day of the month you retain that whole month's interest. you can have co-owners and beneficiaries and when you redeem you can designate which SSN will pay the tax.
没看到fedelity或者其他投资机构有介绍是因为投资机构不卖，要买只能去政府官网。这个介绍很全面：
https://thefinancebuff.com/how-to-buy-i-bonds.html
利息每月自动转存，卖的时候一并拿。