fixed amount, 延長供樓年期,大部分bank都可以(maybe charge 手續費).不過有樓齡限制.一般不可超過35年. for example: if the age of your house is 5 years, and the mortage time is 20 years, that means you can extend 10 years to compensation the interest raising in future.
我冇做過fixed amount, 但try in last year when the interest is downing,不過因銀行要收500手續費所以冇轉到.
in my view, 我不會extend,徐非加息後,over左負擔能力. when you extend the time, that means you need pay more interest to the bank.(利息總數增加).