简言之，重贷合算与否，要看 total interest over the life of the PROPERTY. 从此意义讲，重贷划算否，当然与贷款年限，还剩多少年有关。因此，如果你想付清房贷，do your math. you will save after refi if
- you keep paying what you paid before monthly, or
- you pay off your old loan balance in remaining years under new loan rate, in your example, 4% 20 yr fix.
事实是，许多地主并不想迅速付清贷款，或不打算长期持有，这种情况下，人们更在乎的是降低 monthly payment 以增加现金流. 低利率的重贷可以达到此目的。
