GST & BAS quick calculator
Free calculator for Australian sole traders and tradies: add 10% GST or take it out of a price, estimate G1, 1A and 1B for a Simpler BAS, and check whether you've hit the $75,000 GST registration threshold. Runs in your browser.
The two GST sums everyone needs
- Adding GST to an ex-GST price: multiply by 1.1. $1,000 + 10% = $1,100, and the GST is $100.
- Taking GST out of an inc-GST price: the GST is 1/11 of the total, not 10% of it. In $550, the GST is $50 and the ex-GST price is $500. Taking 10% off $550 gives $55, which is wrong.
What the BAS tab works out
On a Simpler BAS you report three GST figures (see our Simpler BAS guide):
- G1 Total sales: all your sales, taxable and GST-free, either including or excluding GST. You tick which one you used.
- 1A GST on sales: the GST in your taxable sales.
- 1B GST on purchases: the GST credits on business purchases, counting only the business share of anything you also use privately. You need a tax invoice for purchases over $82.50 including GST.
The ATO asks for whole dollars, rounded down, so the calculator drops the cents. It's an estimate for one period. It doesn't handle instalments, adjustments, PAYG, fuel tax credits, input-taxed sales or mixed-supply bills.
Not registered for GST?
The box starts unticked. If you're not registered, don't add GST to your prices or show it on invoices, and you don't lodge 1A or 1B. You can still use the first tab to see how much GST is inside a bill you've paid, and the third tab to check each month whether you're close to $75,000. You reach the threshold if either your last 12 months (this month plus the previous 11) or your next 12 months (this month plus the next 11) comes to $75,000 or more. Then you have 21 days to register. See Do I need to register for GST?
Privacy: the calculator runs entirely in your browser. Nothing you type is sent to us or anyone else, and the page loads no trackers, analytics or third-party scripts. So your figures are still there next time, they're saved in this browser's local storage on your device only. To remove them, clear this site's data in your browser settings.
The calculator
Pick a tab and change the yellow boxes. The example figures are made up, so replace them with your own.
Add or remove GST
Type an amount and choose whether it is inc GST (already includes GST, so the GST is 1/11 of it) or ex GST (excludes GST, so 10% is added on top). Add more lines to total a quote or a bill.
Line by line
| Line | Ex GST | GST | Inc GST |
|---|
GST is rounded to the nearest cent, with half a cent rounding up (ATO rounding rule). Totals add up the rounded lines.
BAS period
On a Simpler BAS you report G1 either including or excluding GST and tick which one you used (ATO).
Sales this period
Business purchases this period
Choose "No GST" for bank fees, wages, super, stamp duty, GST-free items and suppliers who aren't registered for GST. For things you also use privately, only claim the business share (ATO).
How it adds up
The BAS figures are in whole dollars with the cents dropped, as the ATO asks. This is an estimate only. Your BAS uses your actual records and your accounting basis (cash or non-cash).
Your GST turnover, month by month
GST turnover is your total business income (not profit), less any GST included in it and some other sales. If you're not sure what counts, check the ATO page linked below. Leave out the sale of business assets from your projection.
This month and the previous 11 months (actual)
This month and the next 11 months (expected)
Against the threshold
The ATO says you must register within 21 days of reaching the threshold. You reach it if either your current GST turnover (this month plus the previous 11) or your projected GST turnover (this month plus the next 11) is $75,000 or more ($150,000 for non-profits).
Keep your GST records sorted all year
- Sole Trader GST, BAS & Expense Tracker (AU): log income and expenses as you go and get each quarter's G1, 1A and 1B, net GST and a tax set-aside. It also flags purchases over $82.50 that need a tax invoice.
- Tradie Subbie Register + Payments & TPAR Tracker: subbie ABNs, payments with GST, and a whole-dollar TPAR summary.
- Quote Follow-up & Payment Chaser: get paid so the GST is in the bank before your BAS is due.
- Also: Job Costing & Profit Tracker, Tradie Business Tools Bundle, Site Diary + EOT Log, Tool Register + Test & Tag.
Excel & Google Sheets, no macros, one-off purchase. All tools: payhip.com/Andwatco. Free guides: Do I need to register for GST? · Simpler BAS: G1, 1A and 1B · How to quote a job with GST · What a tax invoice must show
Notes
- This is a general calculator that only works from the figures you type. It isn't tax advice and it doesn't lodge anything. Check ato.gov.au or ask a registered tax or BAS agent before you lodge.
- GST rate 10%. Registration threshold $75,000 ($150,000 for non-profits). Taxi and ride-sourcing drivers must register whatever their turnover. BAS figures are whole dollars, rounded down. Rules from the ATO pages below, checked 25 October 2026.
- Calculator built by Andwat Co. Free to use. Andwat Co template store.
Sources
- ATO – Registering for GST
- ATO – Simpler BAS GST bookkeeping guide
- ATO – Instructions for completing your BAS (round down to whole dollars)
- ATO – Tax invoices
Related guides
- Simpler BAS: what goes in G1, 1A and 1B
- Do I need to register for GST? The $75,000 rule
- How to quote a job with GST (Australia)
- What a tax invoice must show (Australia)
- TPAR for tradies: paying subbies and the 28 August report
Other free tools
General information only. It isn't financial or tax advice. Check your own figures and ask a professional if you need to.