Bret's Blog » Amortization Calculator

Even more math…

Bret Whissel — Fri, 02 Oct 2009 19:29:17 +0000

Hi, folks. It has been quite a while since I’ve made any substantial additions to the site. I just added a new document with some new formulas for directly calculating the interest portion of any payment, and for calculating the total interest paid so far. If you’re into math, you might find the Interest Recurrence document mildly useful.

A little Halloween treat

Bret Whissel — Thu, 30 Oct 2008 17:00:48 +0000

I added a little Halloween decoration to the calculator page, for some holiday variety. Thanks to Don Barnett for the cool pumpkin background.

Calculator Printing and Display tweaks

Bret Whissel — Fri, 17 Oct 2008 15:25:05 +0000

I’ve made some slight modifications to the schedule display: alternating rows of the table now have color bands to help identify rows more easily. In the process, I was also able to reduce (slightly) the amount of HTML that’s generated, allowing the schedule to download and render more quickly (though this is hardly an issue for most of us these days).

For people generating hard copies, I made some very minor tweaks as well. I don’t know if it makes things any better or not.

Baubles and bangles and beads

Bret Whissel — Sun, 10 Aug 2008 04:30:50 +0000

Through trial and error I have played with the calculator’s web appearance. I think it looks more attractive, and I hope you do too. I would never claim to be a graphic designer, but I do what I can.

Credits:

Background graphic: squidfingers.com
Design ideas: CSS Zen Garden
Color scheme: inspired by Uncultivated by Mario Carboni
Image editor: The Gimp

Printing Schedules (again)

Bret Whissel — Fri, 08 Aug 2008 18:26:22 +0000

Hi, folks. I’ve heard from a few of you who have said that you have difficulty printing schedules, or that schedules produce a lot of blank pages. I still haven’t experienced this problem myself because I can’t test every browser/printer combination available.

However, I have tried to make some changes to the HTML that the calculator produces. For those of you who had printing problems, please give the calculator a try now, and let me know if things have improved any (or if they’ve gotten worse, or if nothing has changed).

Thanks!

Now printed schedules are just a bit gooder

Bret Whissel — Wed, 30 Jul 2008 16:27:27 +0000

It turns out there is HTML which can indicate which header material should be duplicated across multi-page tables: the tags. So now that I’ve re-learned this and tweaked the calculator again, multi-page tables will have the column headings on each page when printed, provided your browser does the right thing. (I use Firefox for almost all my web-browsing needs.)

More on rate-finding

Bret Whissel — Wed, 16 Jul 2008 19:49:47 +0000

In responding to a question in blog comments about rate-finding, I noticed that the calculator didn’t behave well if the Payment Amount could not pay off the loan after the Number of Regular Payments had elapsed, no matter how low the interest rate. To fix this, I added a test for the condition and have the calculator write an error message if necessary.

It’s a little surprising to still find bugs of this magnitude after all these years. But hey, they’re still getting fixed, one by one.

Mmm, more stylesheet goodness

Bret Whissel — Mon, 14 Jul 2008 18:12:22 +0000

For those of you who like hard copies of your amortization schedules, I have produced a new stylesheet which should make printing the schedule a little less ugly than it may have been before. I still wish there was a way to manage page breaks better on more browsers, but I guess some of the browser builders will need more time to implement all that CSS has to offer. (I would also like for there to be a way to re-start column headings after the first page, but alas, that doesn’t seem to be a possibility with HTML or CSS, unless I missed something.)

The Trials of Moving

Bret Whissel — Mon, 14 Jul 2008 15:13:37 +0000

Well, it has happened. What I have feared the most. Calamity. Pain. Suffering. Ego-shattering. In moving the calculator to its new home, it lost its long-held rank as the number one result for the search “amortization” on Google. It is now number two. I am properly admonished and duly humbled.

As for progress, the calculator page now validates as XHTML 1.0 Transitional. It’s a small thing, but I believe in standards.

Having been truly inspired by the work at the CSS Zen Garden, I will try my hand at making visually aesthetic improvements to the calculator web page. There’s no reason why function can’t also be beautiful. However, my skills as an artist are—shall I be generous?—limited. Someday I’d like to hire the services of a graphic designer to make it REALLY cool and pretty.

Negative Amortization

Bret Whissel — Fri, 11 Jul 2008 16:58:00 +0000

I’ve added a new entry to the FAQ regarding negative amortizations. In the process, I also noticed that some of the summary information produced by the calculator and final schedule row are not completely consistent in the NegAm scenario. I will need to fix these. It is apparent that I missed some sort of symmetry in my calculations here (I probably took a shortcut to minimize computer time, which is just so much gagging at gnats these days).

This is interesting to me because I’ve recently been reading some of the Richard Feynman Lectures on Physics, and he talks a bit about mathematical symmetries. We have such an expectation of symmetry that lack of it in certain contexts may indicate a flaw in our understanding, or sometimes it may lead to the discovery of even more interesting properties. (Amortization is not so glamorous as a fundamental law of the universe, mind you; but I now recognize that had I paid closer attention to a mathematical symmetry in this case, I might have noticed my error sooner.)