BAS Calculator (Business Activity Statement)
Calculate your BAS obligations including GST, PAYG withholding, and PAYG instalments. Enter your BAS field amounts to see your quarterly BAS summary, whether you owe the ATO, or whether you are due a refund.
Based on current ATO GST rate of 10%. Enter GST-inclusive amounts for all sales and purchase fields.
Also useful: GST Calculator for line-item GST checks, PAYG Calculator for payroll withholding, and ATO Interest Calculator if you're dealing with overdue BAS amounts.
Total sales including GST for the period
Exports and other GST-free sales
Capital purchases including GST (e.g. equipment, vehicles)
Other business purchases including GST
Tax withheld from employee wages
Your own income tax instalment amount
Enter your BAS figures to calculate
What is a Business Activity Statement (BAS)?
A Business Activity Statement is a form submitted to the Australian Taxation Office (ATO) by GST-registered businesses. It reports your GST collected on sales, GST credits claimed on purchases, PAYG withholding from employee wages, and PAYG instalments for your own income tax.
If you are registered for GST, you must lodge a BAS — even if you have nothing to report for the period. Most small businesses lodge quarterly, while larger businesses (with turnover above $20 million) lodge monthly.
What does a BAS calculator help with?
Most BAS searches are really about one of three questions: how much GST to pay, how much PAYG to report, and whether the final BAS produces a payment or refund. This calculator is built for that exact workflow, so you can estimate the full statement before you lodge.
How GST is calculated on a BAS
The BAS uses a simple method to calculate your net GST position. All amounts are entered as GST-inclusive totals, and the GST component is extracted by dividing by 11.
GST on sales = (G1 Total Sales − G2 GST-Free Sales) ÷ 11
GST on purchases = (G10 Capital Purchases + G11 Non-Capital Purchases) ÷ 11
Net GST = GST on sales − GST on purchases
Total owing = Net GST + W1 PAYG Withholding + T1 PAYG Instalment
If your net GST is negative (you paid more GST on purchases than you collected on sales), the ATO refunds the difference.
BAS fields explained
G1 — Total sales
Report your total sales for the period including GST. This includes all income from goods sold, services provided, and any other business revenue. Include both cash and credit sales.
G2 — Export sales and other GST-free sales
Report any sales that are GST-free. This includes exports, sales of basic food items, medical services, educational courses, and other items listed as GST-free under the GST Act. These are subtracted from G1 before calculating GST.
G10 — Capital purchases
Report purchases of capital assets including GST. Capital purchases are items you buy for long-term business use, such as equipment, vehicles, machinery, or property improvements exceeding $1,000.
G11 — Non-capital purchases
Report all other business purchases including GST. This covers day-to-day operating expenses such as stock, office supplies, rent, utilities, professional services, and contractor payments.
W1 — PAYG withholding
Report the total amount of tax you withheld from payments to employees, directors, and contractors who did not quote a TFN. This amount is remitted to the ATO as part of your BAS.
T1 — PAYG instalment
Report your PAYG instalment amount. This is a prepayment towards your own income tax (or your company's income tax) based on business or investment income. The ATO provides either an instalment amount or a rate to calculate it.
BAS lodging deadlines
BAS due dates depend on your reporting period:
| Reporting Period | Quarter | Due Date |
|---|---|---|
| Quarterly | July – September | 28 October |
| Quarterly | October – December | 28 February |
| Quarterly | January – March | 28 April |
| Quarterly | April – June | 28 July |
| Monthly | Each month | 21st of following month |
| Annual | Full financial year | 28 October |
If a due date falls on a weekend or public holiday, the deadline moves to the next business day. Tax agents may have different due dates.
Worked example
Sarah runs a small retail business. For the October–December quarter, her figures are:
- G1 Total sales: $55,000 (including GST)
- G2 GST-free sales: $5,000 (basic food items)
- G10 Capital purchases: $11,000 (new point-of-sale system)
- G11 Non-capital purchases: $22,000 (stock and operating costs)
- W1 PAYG withholding: $4,500 (from two part-time employees)
- T1 PAYG instalment: $1,200 (ATO-advised amount)
GST on sales: ($55,000 − $5,000) ÷ 11 = $4,545.45
GST on purchases: ($11,000 + $22,000) ÷ 11 = $3,000.00
Net GST: $4,545.45 − $3,000.00 = $1,545.45
Total owing: $1,545.45 + $4,500 + $1,200 = $7,245.45
Sarah owes the ATO $7,245.45 for this quarter. She must lodge and pay by 28 February (the December quarter has a special extended deadline).
FAQ
What is a Business Activity Statement (BAS)?
A BAS is a form that GST-registered businesses lodge with the ATO to report and pay GST, PAYG withholding, PAYG instalments, and other tax obligations. Most businesses lodge quarterly, though some lodge monthly or annually.
How is GST calculated on a BAS?
GST on sales is calculated as (G1 total sales minus G2 GST-free sales) divided by 11. GST on purchases is calculated as (G10 capital purchases plus G11 non-capital purchases) divided by 11. Net GST is the difference between GST collected and GST credits claimed.
When is my BAS due?
Quarterly BAS is due 28 days after the end of each quarter. For example, the July–September quarter BAS is due 28 October. The December quarter has a special extension to 28 February. Monthly lodgers must lodge by the 21st of the following month.
What happens if I get a refund on my BAS?
If your GST credits on purchases exceed the GST you collected on sales, the ATO will refund the difference. This commonly happens when a business makes large purchases or has significant GST-free sales. Refunds are typically processed within 14 days of lodging.
What is the difference between PAYG withholding and PAYG instalments?
PAYG withholding (W1) is tax you withhold from employee wages and contractor payments and remit to the ATO. PAYG instalments (T1) are prepayments of your own income tax based on your business or investment income. Both are reported on the BAS.
Do I need to lodge a BAS if I had no sales?
Yes. If you are registered for GST, you must lodge a BAS for every period — even if you had no sales or purchases. You can lodge a nil BAS through myGov or your accounting software.
What penalties apply for late BAS lodgement?
The ATO can charge a Failure to Lodge (FTL) penalty of $313 for each 28-day period (or part thereof) that your BAS is overdue, up to a maximum of five periods. Interest (the General Interest Charge) also applies on any unpaid amounts from the due date.
Uses 2025-26 ATO rates.
Tax Accuracy & Sources
This calculator is an estimate tool and may not cover all personal circumstances. For state-based taxes, confirm details with your state or territory revenue office.
Turn BAS numbers into branded business paperwork
BAS reporting sits downstream from invoicing, payroll, and collection. Once you understand the GST and PAYG position, use the branding-ready generators to tighten the operational paperwork that feeds your next BAS.