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Doing the Mortgage Numbers

Here are the numbers, assuming a $180,000 house, 6.875% interest, and a 30-year loan. Property taxes excluded from calculations. BTW, every "mortgage calculator" for Mac OS X absolutely sucks. I did this with some online tools at

$180,000, 6.875%, 30 years
             Monthly    + $50   + $100      Interest
0% Down       $1183     10/31    02/29      $245,906
5% Down       $1124     08/31    11/28      $233,611
10% Down      $1065     06/31    08/28      $221,315
15% Down      $1006     03/31    04/28      $209,020
20% Down       $946     01/31    01/28      $196,725
$180,000, 6.875%, 15 years
             Monthly    + $50   + $100      Interest
0% Down       $1605     07/19    11/18      $109,051
5% Down       $1525     07/19    10/18      $103,598
10% Down      $1445     06/19    09/18       $98,145
15% Down      $1364     06/19    08/18       $92,693
20% Down      $1285     05/19    06/18       $87,240
Payoff dates listed for extra payment options.
Total interest paid is for standard monthly payment.

Of course, if software existed that could more easily let me compare these kinds of things - such as total expense for the + $50 and + $100 columns, I'd list those here as well for a better comparison. Online tools only do so much, it seems.

If anyone's got information about a real "play with the numbers" kind of site, please post the URL in the comments. Otherwise, I might just write something.

8 Responses to "Doing the Mortgage Numbers"

  1. Maybe I'm just being naive because I've never specifically calculated mortgage rates, but couldn't this be done with an excel spreadsheet or something? I don't know the exact formulas, but it doesn't seem like it should be *that* complicated.

  2. I'm sure it could be, but I hate Excel.

  3. Excel and X48 (an HP-48 emulator) both include loan payment calculators, but if you put down less than 20%, be sure to add PMI unless you do something like an 80/15/5 loan. Also, if you do an 80/15/5, the second mortgage would most likely have a higher interest rate than the first.

  4. What exactly 'sucks' about the Mortgage calculators? I've never used one since I can barely afford to buy myself lunch let alone a house. 🙂

    Just curious if its a usability issue, functionality, or something else.

  5. Short answer, Justin: both.

    Some don't have tables. Some don't let you tweak settings (like "additional payments/month"). Some don't show you the total amount of interest paid.

    And some don't do any of that.

  6. This is pretty exciting. I like your table.

    It makes me jealous that you could feasibly just write a program to do all these mortgage calculations for yourself, and then possibly even give it away (or even sell it?) to thousands of Mac users. I would end up using excel and having multiple tables and charts going to figure this out for myself.

    I don't know how to code anything beyond html and the first three chapters of the php manual at, but I'd like to learn. I just don't know where/how this is done besides using manuals, most of which assume that I have knowledge that I don't actually have.

  7. You really want to avoid the PMI. It's basically you paying for insurance for the mortgage company so if you don't pay they collect the insurance. To get out of it you put down 20%, you can actually take out a second loan to do this. If not some companies drop the price on it for every 5% you put down.

    If you don't do the 20% and have the money later to get out of it you need to pay for an inspection and probably a processing fee to drop it. I was highly annoyed at this part.

    Most times the 15 year isn't much different from the 30 other than you pay more (just calculate the 30 year loan but instead of +$100 make it plus $400-$500 and see when it gets paid off (as long as you can pay it off in 15 years without penalties). Just look at your chart above. Then if you have problems you can shrink your payment, if stuck in a 15 it's hard to adjust back to a 30.

    If you aren't going to be there forever look at a 5 year ARM (or 3 year), it's usually a better rate (after 5 years the interest rate starts to fluctuate no more than 2% a year). You can refinance during the loan (depending on your terms) or at the end. My company (HSBC) lets me adjust my rate with a phone call (and a $750 fee), I've done it twice and gone from 6.875% to 4.25% now. That's $1,500 and no hassle, much cheaper than most people's refinance and no paperwork. (I've got good credit which helps too).

    Mortgage rates a bound to go down again so if you're going to refinance sometime anyways, the ARM isn't going to hurt.

  8. Erik, I just sent you a copy of my spreadsheet via e-mail.

    I plugged in a few of your numbers into it.

    Subject was "Do you have excel? Doing the Mortgage Numbers"

    It'll let you play around if you have excel or neoOffice.