關於mortgage多付principal的問題

我們的是跟chase的mortgage，是fixed rate，剛剛開始的時候一個月的interest大概是930多，然後每個月少一塊多一點。後來公司bonus和退稅我分別多付了1000多的principal，發現接下來的那個月的interest一下子就少了20多。
那我就想，要是我一下子多付一萬塊的，是不是每個月的interest就更少了？因為interest是based on本金的嘛。
於是，昨天無聊我就打了個電話給chase問問，結果人家說無論你怎麽多付principal，每個月的interest是不變的。我就很奇怪啦，怎麽可能呢？明明每個月都是在變的啊。難道是我理解錯誤？_:o

[2ndglance]

Let me throw in my 2 cents. :)

1) Mortgage interest rate is fixed. It will not change with how much you owe.
2) Monthly mortgage payment will not change even if you make extra payments. However, the number of monthly payment will be reduced by your extra payments.
3) Monthly mortgage payment are divided into at least two portions to pay for a) interest upto the month (interest payment and b) principle (the money you owe)(principle payment). The interest payment will be reduced by your extra payments due to the reduction in the principle (the money you owe). However, your monthly payment will still be the same. The principle payment will be bigger than before due to the reducton in interest payment.

I hope that it will help.