Mortgage calculations
Introduction
This webpage has JavaScript code built in that makes all the calculations as described hereafter. The calculations are based on the classic TVM (time value of money) algorithm. You should be familiar with the terminologies described herafter to better understand what the resulting values are.
If you want to make more advanced TVM forecasts or calculations you should acquire a real business calculator. This page only provides you with the two most common mortgage calculation solutions. These are: "How much can I lend/borrow when I know the downpayments I can afford?" and "How much will I have to pay each month for a loan of a given amount?".
The currency is irrelevant for these formulas so you can use it for your currency as well as for others. Keep in mind that banks will round up or down the final results according to the smallest currency unit used in your country for these transactions. With this program you can choose the rounding precision yourself.
Download this page
You can use the "View Source" option from your browser to copy this program. BUT: You will be missing some pictures and a lot of subfiles used on the web site.
I recommend you to download a local version available here: mort.zip (13k). Then extract all the files to a local directory and open mort.html with your browser.
NEW! Standalone executable!
I finished writing a Win32 executable that does mortgage calculations even better! It allows to print/save a richtext document that contains the full amortization table with all it's mortgage data.
NOW With INF installation setup!
Download and run this setup.exe to automagically install it into your "Program Files\Mortgage" folder and to create an uninstall item in your Control Panel - Add/Remove Programs!
mortsetup.exe v1.5 (290k).
What the Win32 version has more than the JavaScript web page
- List of currencies with preprogrammed currency rounding (if yours isn't there then just type it manually, it won't harm the calculations)
- Automatic built-in conversion of effective vs nominal intrest
- Rounding of monthly interest can be set according to your country (US = no rounding, UK and many others = round i at 0.001%)
- Periods specified in either months or years
- Saves your calculation results with amort table in an RTF file
- Intermediate yearly amortization details
- Calculation results mimic exactly those of HP-12C calculators (except intrest rounding features).
Mortgage Amortization Table
Intrest calculation part.
The mortgage calculation formula uses the nominal intrest rate whereas banks often mention the effective intrest rate. Check with your bank what type of intrest they mentionned to you. In case of doubt fill in the Effective intrest rate and click on the "Convert to nominal" button to obtain the nominal intrest. The nominal intrest rate will be rounded to the digits chosen on a monthly basis!
The Mortgage
The mortgage calculation will use the Nominal intrest as explained in the previous section.
Fill in at least the number of years to downpay your mortgage. Then you have three options.
- To calculate the payments fill in the amount to borrow and click on the "Calculate" button next to the PMT field.
- To know how much you can borrow fill in the PMT field with the payments you can afford and click on the "Calculate" button next to the PV field.
- Based on a total amount paid at the end of the loan you can calcuate the payments and the loan amount as well with the button "Calculate PMT & PV".
After making any calculation you may click on the "Complete Amort Table" button. This will open a new window with all the data and the complete amortization table.
Please note that for rounding error reasons (or rather to avoid the errors) the PMT will be recalculated up to all decimals (internally). This is why your value will be overwritten in the PMT field in any case.
Please note that this will open only one window. Each consecutive table will replace the previous table in that same window.
The figures
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| using | decimals. |
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| Nominal IR | % |
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