Calculate Mortgage Payment - Posted by Tony James

Posted by John Behle on November 24, 1999 at 11:39:48:

People used to “OOW! and AHH!” when they saw my model4p. One of the first portables. I guess I have a hard time throwing it out because it survived my fire and I developed my original newsletters and software on it.

I was pretty high tech back then. Wrote the text in “scripsit”, put it on a floppy. Used a special program that actually formatted an IBM disk, put the file on the IBM disk, took it to the University, for some reason loaded it into an IBM and reformatted it somehow, took it to the computer center where they had an FT100 attached to a Mac and it read the IBM disk, formatted it in “Word” on the Mac and used their high quality dot matrix printer, then took did some cut and paste, took it to a printer and actually had a newsletter.

Pretty slick huh?

I still have such an aversion to deadlines due to that, that I haven’t published a newsletter for several years.

Besides, some day I’m going to boot that speed demon up just for the games. I like some of them better than all the high tech they have today. Maybe I’ll find an old tape and tape recorder and load up my favorite chess game. That’s why I bought my first computer anyway. I was looking at this wierd thing in the Radio Shack store (Model 1 - 1978) and it beat me in chess. I bought it, took it home and played it until it begged for mercy.

Calculate Mortgage Payment - Posted by Tony James

Posted by Tony James on November 23, 1999 at 14:34:30:

How can you calculate the payments on Mortgages. I have tried many times, but I never seem to be accurate. For example, what would be the mortgage payments on a $40,000 loan, with 8% interest for 30 years? And how do you come up with the answer? I know there is Mortgage calculators online, but I want to be able to do it on Paper or with a calculator.

Re: Calculate Mortgage Payment - Posted by John Behle

Posted by John Behle on November 23, 1999 at 18:53:34:

There are financial calculators as low as $30. To try this on paper or with a regular calculator is a real pain. The formulas for the different variables are not that easy to use. Some involve exponents and Logarithms. I dug all of them up years ago to build a computer program to do the work for me.

There are many free financial calculator programs you can download to your computer or most spreadsheets handle these functions. If you use Excel or Quattro Pro I can provide some for you for no charge.

Re: Calculate Mortgage Payment - Posted by Sean

Posted by Sean on November 23, 1999 at 16:16:51:

Most people would use a special type of calculator for that called a financial calculator. You can recognize these calculators because they have 5 special buttons on them normally marked N, i%, PV, PMT and FV.

When any four of those numbers are known the 5th can be calculated automatically by the computer. In your situation we know the number of payments (N) to be 360 (30 years times 12 months). We also know the present value (PV) to be $40,000. The interest rate (i%) is 8%/12 or .6667%. Finally we know that the future value (FV) at the end of the 30 years should be zero, meaning the loan is entirely paid off.

Once you have all those numbers into your financial calculator it produces the answer you want, the payment (PMT) which is $293.51.

Re: Calculate Mortgage Payment - Posted by MN~Chicago

Posted by MN~Chicago on November 23, 1999 at 16:15:57:


Here are the numbers you provided,
and how to calculate:

N = 360… number of months
I = 8…interest
PV = -40,000…money being loaned (negative)
FV =0…no future value
If you have a calculator , press the PYMT
key to get your monthly payment, $293.51.

Spreadsheets - Posted by Hugh James

Posted by Hugh James on November 29, 1999 at 10:15:56:

I would appreciate the spreadsheet programs if it’s not to much trouble. I have both QuattroPro 8 and Excel 2000 on my system. Is one superior to the other? Your advice is appreciated.

Aww c’mon John, it ain’t so bad! (Here’s the answer) - Posted by drew

Posted by drew on November 23, 1999 at 20:09:07:

Okay, you asked for it! Here is how to figure out the payment for a fully amortized loan (with constant payments, interest rate, and relative humidity)

PMT = PV/([1 - 1/(1+r)^t]/r)

PMT = is the periodic payment (monthly or annually)
PV = Present Value of loan
r = the interest rate per compounding period
t = the number of periods (the ^ means that “t” is an exponent)

Now this ain’t so easy to do in your head, or mine for that matter, but you can grunt and grind through it with a regular old calculator. The problem is you’ll want to solve for other variables (like interest rate or # of payments) and then things get interesting as John mentioned.

Now if all of the Y2K stuff comes crashing down I’m starting a consulting business just calculating this one equation…on paper with a little help from Grandma’s abacus!

FREE ADVICE: Buy a Financial Calculator (even if it’s a $30 TI) and never cast your eyes upon this equation again!!!


P.S. The relative humidity part was an attempt at humor, although it does have some affect on my TI.

Re: Calculate Mortgage Payment - Posted by Lisa

Posted by Lisa on November 23, 1999 at 17:14:30:

Can this be done on a regular calculator?

Available to download for free - Posted by John Behle

Posted by John Behle on November 29, 1999 at 12:18:29:

There are two spreadsheets in both Quattro Pro and Excel format available to download at

The first, called “easycalc” is like the yield worksheet in my books. It has all of the 5 variables and you just enter 4 and it automatically solves for the 5th. The spreadsheet is set up to use “circular references” which normally isn’t desirable, but it works well in this case.

Quattro Pro will just give you a little warning at the bottom (and it shows an error in the different cells until you have entered 4 of 5 variables). Excel goes nuts. So, on Excel you need to turn off the automatic calculation and hit whatever key it is to calculate when you have the numbers entered.

The second spreadsheet handles up to ten uneven cash flows of any length. It also calculates immediately at up to 8 different yields. You control those yields and can change them any time you want.

They are just simple spreadsheets, without documentation, so if you have any questions post them here or when people are interested, there is a chatroom where I can actually demonstrate the program to people.

Is so…! - Posted by John Behle

Posted by John Behle on November 23, 1999 at 21:18:43:

When Y2K comes - or I get my HERF gun - we’ll all have to work those formulas by hand again. I may fire up the TRS80 to pull the other formulas off just so we can all be prepared. Get out your legal pads and sharpen your pencils. We’ll be back in the stone age in a couple months :slight_smile: (just kidding).

No…(nt) - Posted by MN~Chicago

Posted by MN~Chicago on November 24, 1999 at 24:42:05:


Thanks John-They Work Great…(nt) - Posted by Hugh James

Posted by Hugh James on November 30, 1999 at 14:39:50:


Dennis has … - Posted by CarolFL

Posted by CarolFL on November 24, 1999 at 09:09:51:

his Trash 80 hidden in the cellar, I think. Last computer he really used, as far as I can tell!

So you think it will have some utility other than to grace an antique store!!

My father has three Trash 80s in the garage (nt) - Posted by Jack Stivers

Posted by Jack Stivers on November 24, 1999 at 13:12:44: