Quote from piezoe:
Consider Instynct's point. And also recognize that to a first approximation your real mortgage rate = rate - rate of inflation.
Think of it this way. Suppose you borrow $100 at 6% with the interest due up front and the principle due in one year and the inflation rate is 10%. You borrowed $100 of buying power and you returned 6$ of buying power as interest. At the end of the year, because of inflation, an asset that cost $100 when you borrowed the money now costs $110, but you only pay back the original $100. Your lender is out 10$ of purchasing power. Your real cost of the money you borrowed is 6% minus 10% or negative 4%. The lender has in effect paid you 4% (in buying power) to use his money.
That's way you should take into account the inflation rate when deciding whether to pay off a fixed rate mortgage. Assuming your nominal rate is 6.25% and fixed, and with your mortgage deduction is effectively 4.375 %. Then as long as the real inflation rate is greater than 4.375%, which it is right now, you have a negative cost of borrowing and should not pay off the loan. Stretch it out as many years as you can and pay your lender back with inflated dollars.
Debtors benefit from an inflationary economic environment!