BAS Calculator Australia 2025-26
Calculate your quarterly BAS in Australia including GST, PAYG withholding, and PAYG instalments. Enter your BAS field amounts to see whether you owe the ATO or are due a refund.
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 BAS is a form submitted to the ATO by GST-registered businesses. It reports 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. Most small businesses lodge quarterly; larger businesses (turnover above $20 million) lodge monthly.
How GST is Calculated on a BAS
All amounts are entered as GST-inclusive totals; 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 + G11 Non-Capital Purchases) ÷ 11
Net GST = GST on sales − GST on purchases
Total owing = Net GST + W1 PAYG Withholding + T1 PAYG Instalment
If net GST is negative (more GST on purchases than sales), the ATO refunds the difference.
BAS Fields Explained
G1 — Total sales
Total sales for the period including GST — all income from goods sold, services provided, and business revenue. Include both cash and credit sales.
G2 — GST-free and export sales
Sales that are GST-free: exports, basic food items, medical services, educational courses. These are subtracted from G1 before calculating GST.
G10 — Capital purchases
Purchases of capital assets including GST: equipment, vehicles, machinery, property improvements exceeding $1,000 held for long-term business use.
G11 — Non-capital purchases
All other business purchases including GST: day-to-day expenses such as stock, office supplies, rent, utilities, professional services, and contractor payments.
W1 — PAYG withholding
Total tax withheld from payments to employees, directors, and contractors who did not quote a TFN. Remitted to the ATO as part of your BAS.
T1 — PAYG instalment
Prepayment towards your own income tax (or company tax) based on business or investment income. The ATO provides either an instalment amount or a rate.
BAS Lodgement Deadlines
| 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 |
Tip: Lodge electronically through myGov, accounting software, or your tax agent for a 4-week extension on most quarters. The December quarter (due 28 February) does not receive an extension.
Worked Example
Sarah runs a small retail business. October–December quarter figures:
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, due 28 February (December quarter extended deadline).
What is a Business Activity Statement (BAS)?
How is GST calculated on a BAS?
When is my BAS due?
What happens if I get a refund on my BAS?
What is the difference between PAYG withholding and PAYG instalments?
Do I need to lodge a BAS if I had no sales?
What penalties apply for late BAS lodgement?
Tax Accuracy & Sources
Estimates net GST, PAYG withholding, and PAYG instalment amounts for a single BAS period. It does not cover fuel tax credits, wine equalisation tax, luxury car tax, or fringe benefits tax.