回复：强，但Excel的这个功能似乎有个严重错误。

来源: emmmm 于 2009-05-10 02:29:41 [] [旧帖] [给我悄悄话] 阅读数 : (774 bytes)
回答: Formula for calculating mortgage 由 emmmm 于 2009-05-08 14:33:15

This is a very interest discussion. I think it is due to the difference between Mortgage and APR (annual percentage rate).

1. The most accurate compounding is 'continuous compounding' which used in option valuation, such as Black-Schole Model. The formula is: e^rate.

2. For daily compunding as the mortgage providers clami, it should be
(1+daily rate)^365

3. For monthly compuning will be exactly as you said above, (1+monthly rate)^12

4. However for mortgage payment calculating, it is the MORTGAGE RATE used, not the APR:

PV annuity = Amount x (1/r) x [1 - 1/(1+r)^n]. The annual rate / 12 is used.

That is why mortgage providers give both mortgage rate and APR.

Thus, Excel's PMT and IPMT are correct.

所有跟帖： 

• 原来如此，长了见识，谢谢。 -jerff- ♀ 给 jerff 发送悄悄话 jerff 的博客首页 (0 bytes) () 05/11/2009 postreply 08:42:38

• 省事的办法，上这个网下个excel calculator -卫明- ♂ 给 卫明 发送悄悄话 卫明 的博客首页 (168 bytes) () 05/12/2009 postreply 02:45:05

• http://www.simpleplanning.com/ -卫明- ♂ 给 卫明 发送悄悄话 卫明 的博客首页 (0 bytes) () 05/12/2009 postreply 02:55:29

请您先登陆，再发跟帖！