BAS Calculator
Enter your G1 total sales, G2 GST-free sales, G10 capital purchases, and G11 non-capital purchases. The calculator returns 1A, 1B, net GST, and total to lodge, with the working shown.
How BAS GST is calculated
GST on sales = (G1 − G2) ÷ 11. GST on purchases = (G10 + G11) ÷ 11. Net GST = the difference.
Most Australian small businesses with GST turnover under $10 million use the Simpler BAS method: only three sales/purchase fields are required (G1, G10, G11), plus G2 for GST-free sales.
If you collected more GST than you paid, you owe the ATO. If you paid more than you collected, the ATO refunds the difference. Refunds are typically processed within 14 days of lodgement.
BAS due dates 2026
Quarterly BAS is due 28 days after the end of each quarter, with an extension to 28 February for the December quarter.
Tax/BAS agents typically receive a 2-week lodgement extension.
| Quarter | Period | Due date |
|---|---|---|
| Q1 | July – September | 28 October |
| Q2 | October – December | 28 February |
| Q3 | January – March | 28 April |
| Q4 | April – June | 28 July |