BAS Due Dates 2026–27: Every Quarterly & Monthly Deadline

Miss a BAS deadline and two things happen at once: the ATO’s failure-to-lodge penalty clock starts ticking, and any GST you owe begins attracting interest. Neither is dramatic on day one — which is exactly why deadlines slip. A new financial year is the right moment to load every BAS due date into your calendar in one sitting, so here is the complete FY2026–27 schedule, including the agent-extension dates that give most businesses an extra four weeks.

This calendar from Trinity Accounting Practice updates our popular 2026 BAS due dates post for the 2026–27 financial year. Same format, new dates, one Sunday quirk to watch in February.

Quarterly BAS due dates 2026–27 — the table to bookmark

*Agent dates apply where a registered tax or BAS agent lodges electronically and you are eligible under the ATO’s lodgement program. Q2 already includes the built-in Christmas concession (28 February instead of 28 January), so no additional agent extension applies.

Three points worth noting in this year’s calendar:

• 28 February 2027 falls on a Sunday. Under the standard ATO rule, when a due date falls on a weekend or public holiday you may lodge and pay on the next business day — Monday 1 March 2027 — without penalty.
• Q2 is the equaliser. Everyone — self-lodgers and agent clients alike — faces the same end-of-February deadline, because the extra month for the Christmas period is already baked in.
• The agent extension is roughly four weeks on Q1, Q3 and Q4. Across a year, that is about three extra months of breathing room on cash flow and paperwork.

Monthly BAS — the 21st, every month, no extensions

If your GST turnover is $20 million or more (or you have elected monthly reporting), your BAS is due on the 21st of the following month — August’s BAS by 21 September, and so on, all year. There is no agent lodgement extension for monthly BAS, and the December BAS keeps its normal January due date for most monthly lodgers. The same weekend rule applies: where the 21st lands on a weekend, the next business day is the effective deadline.

Lodgement vs payment — two obligations, one date

A detail that catches new business owners: the due date is for both lodging the form and paying the balance. They are separate obligations with the same deadline, and they fail independently:

• Lodge late → failure-to-lodge (FTL) penalties can apply, even if the BAS shows a refund or nil balance.
• Pay late → the general interest charge (GIC) accrues daily on the unpaid amount, currently at a double-digit annual rate.

If cash is tight, the right move is almost always to lodge on time anyway and arrange a payment plan with the ATO for the balance. Lodging on time keeps the FTL penalty away, keeps your lodgement record clean, and makes the ATO far more receptive to a payment arrangement. Hiding an unlodged BAS does the opposite on every count.

What late lodgement actually costs

FTL penalties are calculated in penalty units — one unit per 28-day period (or part thereof) the BAS is overdue, capped at five units for small entities. The Commonwealth penalty unit is $330 for offences from 7 November 2024, making the small-entity maximum $1,650 per late BAS — with the unit value due to be indexed from 1 July 2026, so the 2026–27 figure may rise. Medium entities (turnover $1m–$20m) face double, and large entities five times those amounts. The ATO often issues a warning before penalising a first miss, but a pattern of late BAS is one of the quickest ways to lose access to concessions, payment plans and remission requests.

Worked example — what the agent extension is worth in cash terms

A Hurstville landscaping business owes roughly $18,000 in net GST and PAYG withholding each quarter. As a self-lodger, its Q1 payment leaves the bank on 28 October 2026 — right when October wages and insurance renewals also land. Lodging through a registered agent moves the same payment to 25 November 2026: four extra weeks holding $18,000 of working capital, three times a year (Q1, Q3, Q4). That is the equivalent of a recurring, interest-free ~$18,000 overdraft for about 12 weeks annually — before counting the time saved, the coding errors caught at review, and the fact that the deadline becomes the agent’s problem to track rather than the owner’s. For most businesses the agent fee is a fraction of the value of the float alone.

A Trinity insight from 22 years in practice

After 22 years of BAS seasons, we can tell you which quarter hurts businesses most: Q2. Not because the deadline is tighter — it is actually the most generous — but because it sits at the end of the summer break. Owners switch off in late December, January disappears, and the October–December BAS quietly becomes due in the same week school goes back and cash from the holiday slowdown is at its lowest. Our practice rule, run through Karbon for every BAS client: the Q2 file is reconciled and queued before the Christmas shutdown, not after it. The February deadline should be an administrative formality, not a February scramble.

What this means for you

• If you self-lodge quarterly: diarise 28 October 2026, 1 March 2027 (the Sunday-adjusted Q2 date), 28 April 2027 and 28 July 2027 now.
• If you lodge through a registered agent: your Q1, Q3 and Q4 dates extend to 25 November 2026, 26 May 2027 and 25 August 2027 — but Q2 stays at the end of February for everyone.
• If you lodge monthly: the 21st of each month, no extensions — build it into your month-end close.
• If cash will be short at a deadline: lodge anyway and arrange a payment plan. The FTL penalty punishes silence, not honesty.
• If you have overdue BAS from earlier years: each one can carry up to $1,650 in FTL penalties for a small entity, and old GST credits expire after four years — catch up sooner rather than later.
• If you are still on last year’s calendar: the FY2026 dates are in our previous BAS due dates post.

How Trinity can help

Trinity Accounting Practice lodges BAS as registered tax agents for businesses across Sydney from our Beverly Hills office — which means our clients automatically receive the extended agent deadlines on Q1, Q3 and Q4, plus a reconciliation review before anything is lodged. We run every client’s BAS calendar through Karbon so deadlines are tracked by the system, not by memory, and we handle ATO payment plans where cash flow needs managing. If BAS deadlines have ever snuck up on you, hand the calendar to us.

Put your BAS on Trinity’s calendar — talk to the team →

General advice only. This article contains general information current as at June 2026 and does not constitute tax, financial or legal advice. It does not take into account your personal circumstances, objectives or needs. Before acting on any information in this article, you should consider its appropriateness to your situation and seek professional advice from Trinity Accounting Practice or another qualified adviser. Liability limited by a scheme approved under Professional Standards Legislation.