> If you had taken out a 30-year fixed rate mortgage for $100k when rates were around 1%, you can now prepay it for just $70k, i.e., at around a 30% discount.
This isn't optimal money management. If you have a loan at below market rates, pay it off as slow as possible. Instead of using $70k to pay it off, invest the $70k in something that pays more than the 1%. You'll monetarily be much better off.
In other words, borrow money at a lower interest rate, and invest it at a higher interest rate. You make money on the difference.
A friend of mine who I helped coach through financing his car, did just that. The interest rate at the time was the market rate, and I advised him to accelerate his car payments. But interest rates have risen so much, I advised him to switch to making minimum payments. He caught on quick :-)