Free BAS calculator for Australian businesses. Estimate your quarterly Business Activity Statement obligations including GST collected (1A), GST on purchases (1B), net GST payable or refundable, PAYG withholding, and PAYG instalments. Helps prepare for ATO lodgement.
Total tax withheld from employee wages
Total BAS Payable
$0.00
Payable to the ATO
Net GST
$0.00
GST payable
For Australian businesses
Invoicing, GST tracking and BAS-ready summaries, done automatically, free to start.
The Business Activity Statement is the primary way Australian businesses report their tax obligations to the ATO. If you are registered for GST, the ATO issues you a BAS for each reporting period, and for most small businesses that means quarterly. One statement rolls up several obligations: GST you have collected and paid, PAYG withholding from employee wages, PAYG income tax instalments, and (for some businesses) fuel tax credits, wine equalisation tax, or luxury car tax.
This calculator estimates the three amounts that make up almost every small-business BAS: net GST (labels 1A and 1B), PAYG withholding (label W2), and any PAYG instalment (label T7).
Every box on the BAS has a label. These are the ones most small businesses deal with, and where each number comes from:
| Label | What it is | Where the number comes from |
|---|---|---|
| G1 | Total sales | All sales for the period including GST, plus GST-free and input-taxed sales |
| G2 | Export sales | GST-free exports of goods and services (full reporting method only) |
| G3 | Other GST-free sales | Domestic GST-free sales such as most basic food and some health and education services |
| G10 | Capital purchases | GST-inclusive cost of equipment, vehicles, and other capital items |
| G11 | Non-capital purchases | GST-inclusive trading stock and everyday running expenses |
| 1A | GST on sales | 1/11th of your taxable sales: the GST you owe the ATO |
| 1B | GST on purchases | 1/11th of your creditable purchases: the GST credited back to you |
| W1 | Total salary and wages | Gross payments subject to PAYG withholding, before tax is taken out |
| W2 | Amounts withheld | The tax actually withheld from W1 payments, passed on to the ATO |
| T1 | PAYG instalment income | Business and investment income for the period, if you use the instalment rate method |
| T7 | PAYG instalment amount | The fixed pre-payment of income tax the ATO calculates for you |
Since Simpler BAS became the default, businesses with GST turnover under $10 million only report G1, 1A, and 1B for GST. The other G labels remain useful for your own records (this calculator uses them to keep the 1A estimate accurate), but they no longer have to be reported to the ATO.
GST in Australia is 10%, so the GST inside any GST-inclusive amount is 1/11th of it. Your total BAS amount uses these formulas:
GST on sales (1A) = (G1 total sales − G2 exports − G3 GST-free sales) ÷ 11
GST on purchases (1B) = (G10 capital + G11 non-capital purchases) ÷ 11
Net GST = 1A − 1B
Total BAS = Net GST + W2 PAYG withholding + T7 PAYG instalment
If you just need the GST component of a single price, the GST calculator adds or removes 10% GST instantly, and the PAYG withholding calculator works out the tax to withhold from an individual pay run.
An electrician finishes the October to December quarter with $50,000 of GST-inclusive sales (no exports or GST-free sales), $22,000 of GST-inclusive purchases ($5,500 of that was a new capital tool purchase, so G10 = $5,500 and G11 = $16,500), $11,000 of gross apprentice wages (W1) with $3,000 of tax withheld (W2), and a $1,500 PAYG instalment notified by the ATO (T7).
GST on sales (1A) = $50,000 ÷ 11 = $4,545.45.
GST on purchases (1B) = ($5,500 + $16,500) ÷ 11 = $2,000.00.
Net GST = $4,545.45 − $2,000.00 = $2,545.45 payable.
Total BAS = $2,545.45 + $3,000 W2 withholding + $1,500 T7 instalment = $7,045.45 payable to the ATO.
That statement covers quarter 2, so it is due by 28 February. If 1B had exceeded 1A (common in a quarter with a big equipment purchase), the GST difference would come back as a refund and reduce the total payable.
Quarterly BAS due dates are set by the ATO and follow the same pattern every year:
| Quarter | Period covered | Due date | Lodging via a tax or BAS agent |
|---|---|---|---|
| Q1 | 1 July to 30 September | 28 October | 25 November |
| Q2 | 1 October to 31 December | 28 February | 28 February (no further extension) |
| Q3 | 1 January to 31 March | 28 April | 26 May |
| Q4 | 1 April to 30 June | 28 July | 25 August |
The quarter 2 due date is already pushed out to 28 February to cover the Christmas and New Year period, which is why agents receive no further concession for it. When a due date lands on a weekend or public holiday, you can lodge and pay on the next business day. Businesses on a monthly cycle (compulsory once GST turnover reaches $20 million) lodge by the 21st of the following month. Always confirm your own dates against the ATO due dates page linked in the sources below, or your ATO Online Services account.
Once you have your figures, there are three ways to get the statement to the ATO:
OneBookPlus is built for that third path. The OneBookPlus finance suite produces a quarterly BAS and GST report with the full G-code breakdown (G1, 1A, 1B, G10, G11, W1, and W2) straight from your live invoice, expense, and payroll data, so the numbers in this calculator come pre-assembled every quarter. And the ATO Tax Lodgement app is built as a registered Digital Service Provider lodgement path via the ATO's secure SBR gateway, with mandatory MFA, pre-submission validation, and 7-year audit logging, so the reviewed figures can go to the ATO directly rather than being retyped into the portal.
Keep good records throughout the quarter, reconcile your bank transactions regularly, ensure all invoices include GST where applicable, and claim GST credits on all eligible business purchases. Watch the common traps: GST-free sales still belong in G1, purchases from unregistered suppliers carry no GST credit, and you need a tax invoice on hand for any credit claimed on purchases over $82.50. Using accounting software like OneBookPlus automates BAS calculation from your invoices and expenses, and lodging a nil BAS on time when there is nothing to report keeps penalties off the table.
A Business Activity Statement (BAS) is a form submitted to the ATO to report and pay several tax obligations including GST, PAYG withholding, PAYG instalments, and other taxes. Most small businesses lodge BAS quarterly.
Quarterly BAS is due 28 days after the end of each quarter: 28 October (Q1), 28 February (Q2), 28 April (Q3), and 28 July (Q4). The Q2 due date is extended to 28 February to account for the Christmas/New Year period. If you lodge electronically via a registered tax/BAS agent, you may receive a further extension for some quarters.
GST turnover under $20 million: you generally report quarterly (the default for most small businesses), with the option to report monthly. GST turnover of $20 million or more: monthly reporting is compulsory. Some businesses report annually if voluntarily registered and turnover is under the $75,000 ($150,000 non-profit) registration threshold. Always confirm your cycle on your ATO Online Services dashboard.
Label 1A is the GST on sales, the total GST you've collected from customers. Label 1B is the GST on purchases, the GST you've paid on business purchases. The difference (1A minus 1B) is your net GST payable to the ATO, or refundable if 1B exceeds 1A.
GST in Australia is 10%, so the GST included in a GST-inclusive amount is 1/11th of that amount. To find GST on sales (1A), divide your taxable sales (G1 minus G2 exports minus G3 GST-free sales) by 11. To find GST on purchases (1B), divide your total GST-inclusive purchases (G10 capital plus G11 non-capital) by 11. Example: $50,000 in taxable sales ÷ 11 = $4,545.45 of GST.
To remove 10% GST from a GST-inclusive price, divide the total by 11 to get the GST component, then subtract it, or simply divide the total by 1.1 to get the GST-exclusive (ex-GST) price. Example: a $110 invoice contains $10 GST ($110 ÷ 11) and $100 ex-GST ($110 ÷ 1.1).
PAYG instalments are pre-payments of your expected income tax. The ATO calculates an instalment amount or rate based on your most recent tax return. This is separate from PAYG withholding (tax withheld from employee wages).
Yes, if you're registered for GST, you must lodge a BAS even if you have no sales or purchases for the period. Lodge a 'nil' BAS to avoid penalties.
You can lodge it yourself through ATO Online Services for business (sole traders can use the ATO app or myGov), by mail, or directly from SBR-enabled accounting software. Alternatively, a registered BAS or tax agent can prepare and lodge on your behalf, which also gives you extended due dates for most quarters. Whichever channel you use, keep the records behind every label for five years.
The ATO can apply a failure-to-lodge penalty, calculated in penalty units for each 28-day period the statement is overdue (up to a maximum of five periods), and general interest charge accrues on any unpaid amount. If you can't pay in full, lodge on time anyway: lodging and paying are separate obligations, and the ATO offers payment plans for businesses that engage early.
W1 is the total of salary, wages, and other payments subject to PAYG withholding for the period, before any tax is taken out. W2 is the tax you actually withheld from those payments. Both come straight from your payroll records: W1 is the gross figure, W2 is the withheld tax you pass on to the ATO.
Simpler BAS is the default GST reporting method for businesses with GST turnover under $10 million. You only report three GST labels: G1 (total sales), 1A (GST on sales), and 1B (GST on purchases). Labels G2, G3, G10, and G11 no longer need to be reported to the ATO, though this calculator still accepts export and GST-free sales so your 1A estimate stays accurate.
Sources & methodology
This estimator follows the ATO Simpler BAS GST labels for FY 2025-26: GST on sales (1A) is the GST included in your taxable sales (G1 less G2 export and G3 GST-free sales) at the 1/11th of GST-inclusive amounts, GST on purchases (1B) is 1/11th of your capital (G10) and non-capital (G11) purchases, and the total payable adds PAYG withholding (W2) and any PAYG instalment (T7). Figures are computed in your browser, nothing you enter is stored or sent to a server.
Authoritative sources
Reviewed by Bishal Shrestha, Founder of OneBookPlus, 10+ years building tools with Australian tax-agent and BAS-agent practices. Last reviewed and updated: June 2026.
Disclaimer: This calculator produces estimates only and is not tax advice. Tax outcomes depend on your individual circumstances. For decisions that affect your tax position, consult a registered tax agent or the ATO directly.
OneBookPlus handles invoicing, GST tracking, BAS prep, and ATO lodgement automatically.
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