The free online GST and GST Free Portion Calculator! Provided here for your use. Please make sure you report any issues with the calculator in the comments below. Enjoy your calculations!

I wrote this simple little script in JavaScript to help me calculate Australian GST (10%) today. Being such a useful little script, I thought I would post it.

Please feel free to use this script as your require, if you wish to have this script on your own website please post an acknowledgement and link back to this page.

**How to Calculate GST the hard way (using you know, numbers and shit)**

If you have something without GST, and you need it with GST, you add 10%. Which is easilest done on a calculator by multiplying your amount by 1.1 (which is really saying mister Calculator, give me 110% of this amount).

`$100 * 1.1 = $110`

To go the other way, let's say we have $110, which includes 10% GST already. Working out how much is the GST part is quickly done on a calculator by dividing by 11. Not 10 you say? No, 11. Because easiestly explained, before GST you had 10 parts of a number, the "extra" 10% is another "part". So we need to work out what that part is.

`$110 / 11 = $10`

Huzzah! We have the GST component of an amount! Now, we need to take that GST part from our original amount of $110 to get what the amount is without GST.

`$110 - $10 = $100`

Perfect :-)

But seriously, why do all this manual work when this GST calculator does it for you?

Last Updated 04/03/2014: Fixed floating point arithmetic (Loss of 1c on some calculations). Thanks to Michael for pointing it out.

Thanks for the detailed breakdown of GST and how to calculate it. The example you provided makes it much easier to understand the process. I’ve been using online GST calculators for a while, and they’re definitely a time-saver, especially when dealing with multiple transactions. It’s great to see tools like these becoming more accessible for small business owners!

Hi Darren, the GST-free component calculator appears to be not working. Any numbers I use keep coming up with “Unable to Calculate” in the GST Free amount field. I am trying to work out the amount for the following info: $3942.00 Total & $518.18 GST. I am using Google Chrome on the latest version.

Chrome is up to date

Version 113.0.5672.127 (Official Build) (64-bit)

I use this all the time as a bookkeeper and I hope you are still updating this tool as it is a god send for my business.

Hi!

I’m still about. Just your numbers, aren’t making sense in order to have a GST free portion.

At $3942.00 total including GST, the GST portion must be no larger than $358.36 – when you give it more than 10% of the total as a stated GST Free portion, seems there’s potentially other tax included in this $518.18 that my calculator can’t account for.

If there is a GST free portion for your numbers, GST stated would have to be less than $358.36.

Is the $3942 before tax potentially? In order to get $518.18 of GST, the total would have to be $5700 to have $0 GST free, you’d need to see a total of more than $5700 to then start having a GST free portion of tax. (Say at $5800, GST $518.18, $100.02 would be GST free).

Hope that helps. Cheers,

Hi Darren,

Would it possible to ever have the option of 5 decimal places after the zero, say $0.03608 and the ability to add GST onto this. I am attempting to compare energy tariffs, and all GST calculators online ever use 2 decimal places. I’m not sure if this is necessary or not, perhaps it is so little it doesn’t make a difference – but would like to hear your thoughts on this.

Thanks

You could on a calculator. I wouldn’t update this one to support as such. As for if it makes a difference, if you’re talking about the rate of electricity for a house, no I wouldn’t stress about it whatsoever. If you’re spending hundreds of thousands of dollars, then maybe, but use a calculator.

Darren,

Forgive my ignorance but what is the math behind the GST free portion when only the Total and GST amount is know.

Thanks

Samantha

To get GST, times by 10% ( * .1) * .1) + / 11 – ( / 11)

To see total with GST, (

To see GST out of an amount that already includes GST,

To see total excluding GST out of an amount that already includes GST,

There’s a bit of a speel on the page about .1 and /11 and how it works.

Poor ole new zealanders

Paying 50% more than Australians in G.S.T.

Great tool, use it daily.

G’day Darren, the GST free component calculator is not working. I use this infrequently but it is so helpful rather than working out the numbers and shit!

Seems to be calculating as expected for me.

What numbers are you trying to run?

Is your issue browser specific?

I just love this page ……. I used to detest having to do my BAS but now I just zip thru it ….. you should develop an App ….. making it even easier for us lazy scoundrels lol . Thanks so much for your help . Kathy

Love this site because my maths is hopeless.

You have saved my scrawny neck so many times and for years. 😀

We have been in self-employment for over 35 years.

Thank you very much.

I think I have been using this for about 5 years and still are very grateful!!!!! Thank you

Hi Darren, I find this calculator very helpful when pricing jobs.

Thank you.

Great to hear =D Love it when people find this stuff useful.

This site is a gem. Thankyou so much.

Always come back to this site whenever i need anything GST related/

Coming back to Darren Nolan’s GST calculator.

I love it. Very useful.

luv your style! simple to the point easy to understand. straight talk makes sense of the most confusing issues. well done!!

Thank, helped a lot.

http://romelpaperworks.com.au/

just started will really help thanks

Hi Darren, just started a new business, really rubbish at well most of it, so finding your app is a good good thing, thanks, Happy Days.👌

Life saver normally done on computer had to do manually couldn’t think straight. Karen

Hi, If we divide a gross amount by 11 to find 10% GST, how can we translate this simple exercise to another %.

110.00 / 11 = 10.00

Say 15%.

Gross amount 115

how do we easily calculate the % Amount within the 115 using the 10% example above?

Thanks,

Judy

The short-term answer is https://darrennolan.com/2010/11/19/new-zealand-gst-calculator/

The long term answer is I’ll write you up a nice proper calculation for it shortly.