-1 to alliant. Had pretty bad experience signing up, they opened the account then closed them, had multiple errors in their website, support wasn't helpful at all.

That was a couple years ago, maybe i should try again

You can. Only deduct (married) if you pay more than 10-15k of interest a year? Or am I missing something (itemized deductions is now at 20k limit or so).

Edit: and since you need to pay taxes on dividends in bank accounts, you would need something like 3.5-4% interest to match the gains from prepaying the mortgage at 2.75%?

Interest would never match it.

But ignore the interest deduction. Even if you got a 4% return and paid long term capital gains you’d be ahead.