[PopAlongKid]

1. The IRS web page is not authority. See the Internal revenue code §6654. Failure by individual to pay estimated income tax (a) Addition to the tax. Like I said, it is officially (by law) called an addition to tax, not a penalty.[0] Further, it is calculated as an interest charge. There is not any further interest charged on the interest. Yes, there are actual penalties such as Failure to File/Failure to Pay that do accrue interest, but this is not either of those.

[0]https://www.law.cornell.edu/uscode/text/26/6654

2. The HSA is just a holding account. You can either pay for health expenses such as insurance pre-tax each year, or you can put it in a HSA and delay the payment. In either case, you only get one tax deduction, not two. The ridiculous claim is to say for a $1K contribution to HSA, you get a $1K tax deduction, then you get another $1k tax deduction when you take it out - not true.