The FooDoo Lounge

Tax Calc 1.1


Tax Calc is a utility for people who have to calculate or split figures that include a sales tax, like GST or VAT.

It calculates any two components of a sale or purchase figure if supplied with the third. If, for example, you know you paid $495 for an item and that the tax rate is 10%, it will calculate the tax paid ($45) and the base selling price ($450). If all you know is the tax rate and how much tax you paid, it will tell you the base and total prices, and so on. Tax Calc can be used to place the desired value on the clipboard, so that it can be pasted into another program or document.

Tax Calc screen shot

I wrote this sometime after GST was introduced in Australia because I often get invoices that don't show the nett price, though I need to enter this in the accounting package I use. It's easy enough to do with a calculator obviously, but I'm not all that keen on doing boring things repeatedly when I can have fun writing a little jigger to do it for me. I recently updated it to support different tax rates, so that it may hopefully be of some use to other people who deal with such things. Tax Calc could also be used by people who buy and sell things, to calculate markups.

I would prefer something that was able to recognise the characters on a page I'm looking at, pipe them through my code and deposit the result neatly into the right place in MYOB for me, but I haven't worked out how to get AppleScript to do that sort of thing yet. This is a start at least. ;-)


As long as you are using a compatible OS and have the Dialog Director scripting addition installed (see System Requirements), just double click it and go: Enter a numeric figure in any field and the others will be calculated as you type. Each field has a corresponding "Clip" button which can be used to place that value on the clipboard.

Changing the tax rate requires a recalculation, but Tax Calc has no way of knowing which is the reference value until you enter something in one of the other fields. The value of that field is then used to recalculate the other two. If you wish to recalculate using one of your existing values, enter a zero at the end of it, if it has a decimal point, or a decimal point if it doesn't.

Calculated numbers are displayed and sent to the clipboard in currency format - precision to 2 decimal places - so they should be able to be used directly by just about anything*.

There is a status display in the lower left corner which confirms clipboard actions and reports calculation errors. Tax Calc remembers its window position, so you can leave it out of the way somewhere or just launch it as required. I have an alias to it in my Apple Menu.

* Technically speaking, the value that is placed on the clipboard is text containing some numbers and a full stop (period). Everything I've used that deals with numeric values will accept this as a number, though it's actually what I'd call a string.

System Requirements

Tax Calc is designed to run on any Mac using OS versions 8.5 to 9.2.x (and Classic under OSX), with a standard installation of AppleScript, as long as you have the free Scripting Addition Dialog Director installed.

For reasonable performance, I recommend PowerPC machines running a 604, G3 or G4 processor at 200 MHz or higher. This includes all iMacs & iBooks and all recent PowerMacs & PowerBooks.

It should work fine on older (pre 8.5) systems as long as the Jon's Commands osax is also installed, but it will be pretty slow on older hardware.

Bugs & Limitations

It doesn't always deal with huge numbers well, but the upper limit actually depends on what version of AppleScript you're running. Running under OS9.1 and AS1.6, it calculates total values up to about $99,999,999.00 correctly.

If you need to calculate figures larger than this, then you will need the Deluxe version, gold plated and personalised with your firm's name and anything else you want. Tax Calc Deluxe is available now for only $AU999 including GST. ;-)


Tax Calc is kiteWare. Please read the licence before using the software.

Download Tax Calc (91K)

Additional Information for Scripters

My General Terms for Code Use are here. Please read them if you intend to make use of any of the code.



The FooDoo Lounge is Copyright © Richard Morton 2002-2005

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