有没有公式验证银行Mortgage的正确性

pangpang

如题，正常应该是每月，或每两周还款额固定。应该是用于还利息的部分越来越少，还本金的部分越来越多。但我的银行给的summay我看不懂。我已经多还了本金（每年做多多还2万），但银行还利息的部分并没有减少。是怎么回事？有没有公式自己算？否则银行弄错了，自己也不知道。

taoyuan

除非你refinance，要不你还得按照原来的contract还款，但是你多还的部分就去缩短贷款年限了。

黑山老妖

Depending on your contract. Please read that first to see the extra payment indeed reduce your principle. Some contracts don't allow you to do that.

Also your extra repayment, if it's only a small amount, doesn't make too much difference when the base figure is so big. It takes a few years to see the real difference. Compounding is the key here.

The other thing to keep in mind is if you pay every month, the number of days in a month varies. So one month will be more than the next simply because one has 31 days and the other has 30 days.

pangpang

谢谢楼上答疑。看了合同，还是搞不懂。下面是部分合同条文。
How we calculate interest charges:
3.4.the daily percentage rate for a day is the annual percentage  rate for that day under this contract divided by 265 or 366 in a leap year
3.5  Interest charges for each day are calculated by applying the applicable percentage rate to the relevant portion of the amount owing on your loan balance at the end of that day
3.6 Interst charges accrue daily from and including the settlement date and are debited to your loan balance (so increasing the amount owing on your loan balance) as decribed in 3.7
3.7 we debit interst charges: a) on the last day of each repayment period. b) on the day you repay the total amount owing in full.
PART 4: PREPAYMENT
4.19 You may prepay the whole or any part of the total amount owing at any time up to $20,000 in any year or during fixed rate period.
从前几个月的summary 看，还利息的部分是逐渐减少的，虽然减少得很慢。但上个月我多还了本金（prepayment), 还利息的部分反倒又多回去了。郁闷！