BAS for beginners: what it is and when it's due

What a BAS is

A Business Activity Statement is the form GST-registered businesses lodge, usually each quarter, telling the ATO the GST you collected on sales and the GST you paid on purchases. The difference is what you pay, or what's refunded to you. If you pay PAYG instalments, they usually ride on the same form. If you're not registered for GST and don't pay instalments, you don't lodge a BAS at all.

Quarterly due dates for 2026–27

Quarter 1 (July–September) is due 28 October 2026. Quarter 2 (October–December) is due 28 February 2027 — everyone gets the extra month over summer. Quarter 3 (January–March) is due 28 April 2027. Quarter 4 (April–June) is due 28 July 2027.

When a due date falls on a weekend or public holiday, you have until the next business day. Lodging through a registered tax or BAS agent generally buys extra time on most quarters — one of the practical perks of having one.

The labels, decoded

G1 is your total sales for the period. 1A is the GST you collected on those sales. 1B is the GST you paid on business purchases and can claim back. The headline result is 1A minus 1B. Most small businesses report on the simpler method, which only asks for those three numbers plus a couple of flags.

Cash versus accruals matters here: on the cash basis you report GST in the quarter money actually moved; on accruals, in the quarter the invoice was issued. Most small sole traders use cash — it matches the bank account, and you never remit GST on an invoice that hasn't been paid.

The two habits that make BAS painless

First, keep the GST you collect out of your spending money from the day it arrives — it was never yours. Second, keep the books current monthly rather than rebuilding the quarter in the last week of October. A BAS assembled from up-to-date books is a fifteen-minute check; a BAS assembled from a shoebox is a weekend.

And the standing rule: software prepares, people lodge. Kelpie gets your figures BAS-ready; the lodgement itself is yours, or your registered agent's.