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.

I use this almost daily and it saves me soooo much time! Thanks Dazz! Happy to donate.

Thanks Kate! Really appreciate it ðŸ˜€

Return link now appears on my web site. Have a great weekend!

Let me know if you ever head up this way and there’s a discount waiting.

You’re wonderful thank you ðŸ˜€

I love this, thank you so so much.

I still can’t work out how to add the GST auto on a column on my spreadsheet.

Thank you so much for this!

Thanks Dazz,

My boss cant believe how easy i converted all his prices.

Cheers,

Chris

Nice one, thanks. What other stuff have you written???

Um. Paypal Calculator. NZ Calculator. Many undisclosed projects for many different people? ðŸ˜€

Great calculator, really useful and bookmarked!

Good one Dazz!! Thanks much appreciated

Hey, I am having troubles with your AWESOME calculator…the last few times when I have used the GST Free Portion Calculator it comes up the the error “Unable to Calculate”. It could just be the Telstra bill is wrong….. Thanks

Hi Emma,

This typically happens if you copy in the $ signs (they’re not numbers, and at this stage the system doesn’t automatically remove them). Alternatively, try adjusting the GST amount down slightly and see if it calculator begins to calculate again.

Further to this again (wooo on a roll), pass me your numbers and I’ll take a look.

Thanks.

Thank you for this! Have bookmarked and use it quite regularly =)

Thanks for the very handy script. Nothing I hate more than trying to work out the GST component of an inclusive cost.

Thank you my calculator cracked up so this was great!!!!

Thank you very much from a very mathematically challenged technophobic individual ðŸ™‚

Now just to find a business program that will work for me!!!

Thanks for this GST calculator. I use it every day!

Thanks again for your GST Calculator.

I keep coming back again and again to use it.

Fantastic tool.

Thanks heaps.

Thanks heaps – yeh if gst changes you will have a lot of angry people comming to search for you.

ðŸ˜›

Thank you so much for this! Seriously this solved all my GST issues ðŸ™‚

Hey Darren, this is awesome. Meant I could ditch Xero and make invoices a really strange way using Adobe Illustrator. Nevertheless, as soon as I can I am going to help with your caffeine addiction. Thanks again. Brad

yay I love caffeine! \o/

YOU ARE THE BEST! You have obviously had to try and book a Telstra bill!

Sure have xD

Hey Darren,

I have just got a new laptop and the first thing I added to my bookmarks bar was your page. I use this calculator a lot – it really helps me with my accounts! Thanks so much!

Cheers

Nik

Glad to hear it ðŸ˜€

this is OK when GST is 10% but what if the GST increases to 12% or 12.5% etc

would love to know the formula for this

your explanation of the 10% is really great and understandable

well done

When GST for Australia changes, I’ll update the site. Otherwise there’s something like 6000 unique visitors (according to google) that’d be really upset with me!!

To get really technical when adding different percentages (let’s say, for markup on a product, or if GST does finally increase) we can always do things the long way.

Going forward is easy. So whatever the percentage is, we can add that on our calculators to get the new “gst” total amount.

On your calculator, 100 + 20% = $120. As you’d expect. Is also the same as 100 * 1.2 (or 1.15 for 15% or 1.125 for 12.5%).100% “gst” would work out to 100 * 2. So if your calculator doesn’t have the % function, you know now how to convert it accordingly to a real value.

Backwards is fun!

We know it’s 20%. So a whole part is 1. 20% of a whole part is .20. So we get ourselves 1.2. We can divide 1.2 from our marked-up amount, and get back to $100. Here’s how.

120 / 1.2 = 100. Excellent. Did you notice using this format we can do it with any percentage?

110 / 1.1 = 100. 1.1 is the real 10% GST. \o/

THE FULL STORY MATH!

120 is our end price. x is the original amount. And we know that 20% of that (or 0.2 * amount) is the markup/”gst” amount.

120 = x + 0.20x

120 = 1x + 0.20x (because x by itself really is 1x)

120 = 1.20x (cause we’re awesome and know 1 + 0.2 = 1.2)

120 / 1.20 = x (dividing both sides of equation by 1.20 to give us x by itself.)

120 / 1.20 = 100 WOOOO. Our original amount ðŸ™‚

But that’s the long way. There’s many different ways to solve a problem.

Now as I’m dreadfully tired, I’m heading to bed. But I _think_ there’s no errors in my math tonight. ðŸ˜€

And I apologise dreadfully for Wordpress’s lack of line breaks in their current version of comments… Makes my comment look like a giant wall of text.

Well Australia is only 10% so you do not have to worry unless you leave the country

Thanks Darren, this is a godsend for someone who is mathematically challenged. It means I don’t have to check my figures 4 times!! cheers.. Pamela

how do you deduct the GST from the total amount using a calculator.

Cheers

GST Amount / 11 gives you the GST portion, then take that from the total amount.

$100.00 without GST, is a total of $110 with GST (GST being 10%). So $110 / 11 = $10. Take that from the GST inclusive amount of $110, and we’re back to $100. =D

I can’t actually believe I didn’t have it on this page already. Added ðŸ™‚

This helped so much!! I’m horrible at math so thank you, very much appreciate you’re time and work on producing this fantastic little calculator ðŸ™‚

Finally got the answer I wanted, thank you ever so much. Cheers

Hurray! \o/

Very helpful, quick, easy and simple to use ðŸ™‚