关于mortgage多付principal的问题

我们的是跟chase的mortgage，是fixed rate，刚刚开始的时候一个月的interest大概是930多，然后每个月少一块多一点。后来公司bonus和退税我分别多付了1000多的principal，发现接下来的那个月的interest一下子就少了20多。
那我就想，要是我一下子多付一万块的，是不是每个月的interest就更少了？因为interest是based on本金的嘛。
于是，昨天无聊我就打了个电话给chase问问，结果人家说无论你怎么多付principal，每个月的interest是不变的。我就很奇怪啦，怎么可能呢？明明每个月都是在变的啊。难道是我理解错误？_: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.