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BAS / GST timing for builders

Builder BAS / GST timing: quarterly cycle, due dates, GST on progress claims, retention treatment, and the tax-account discipline that prevents ATO trouble.

By Chalkline. Last updated 15 May 2026. Verified 15 May 2026.

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TL;DR

A residential builder above the $75,000 GST threshold reports GST on a quarterly Business Activity Statement (BAS) cycle. The four BAS quarters end September, December, March, and June; lodgement is due 28 days after each quarter end (Oct 28, Feb 28, Apr 28, Jul 28) unless an extension applies. GST sits on most builder transactions: progress claims OUT (you owe ATO 1/11th), supplier invoices IN (you claim back 1/11th paid). The trap is treating collected GST as today’s cash and being short come BAS day. A separate tax account swept on every stage payment is the discipline that prevents most BAS incidents.

Who must register for GST

The ATO threshold for compulsory GST registration is $75,000 gross turnover (excluding GST) in any 12-month rolling period. Residential builders well above this threshold register on company incorporation. Builders sub-threshold can voluntarily register; most do, because the GST credit on inputs (materials, fuel, subscriptions) accumulates worthwhile cash back.

Cash basis vs accrual basis

Builders can elect GST reporting on either:

BasisWhen GST is reported
CashWhen you actually receive payment / make payment
AccrualWhen you issue an invoice / receive an invoice

Cash basis is allowed up to $10M annual turnover (small business) and strongly preferred for builders because:

  • Progress claim issued doesn’t equal cash received; cash basis only triggers GST liability when paid.
  • Trade invoice received doesn’t equal cash paid; cash basis only triggers credit when paid.
  • Matches builder cashflow reality.

Most accounting software (Xero, MYOB, QuickBooks) supports both; you elect once at GST registration.

The BAS cycle

Quarterly cycle (most residential builders):

QuarterPeriod coveredLodgement dueExtension (BAS agent / monthly elect)
Q11 Jul to 30 Sep28 Oct25 Nov
Q21 Oct to 31 Dec28 Feb28 Feb (no extension)
Q31 Jan to 31 Mar28 Apr26 May
Q41 Apr to 30 Jun28 Jul25 Aug

Monthly cycle is mandatory above $20M annual turnover OR if elected by the builder for cashflow management reasons (most residential builders don’t elect monthly).

What’s on a BAS

The BAS form for a residential builder typically reports:

LineWhat it covers
G1Total sales (GST-inclusive) for the period
1AGST collected on sales (G1 / 11)
G10Capital purchases
G11Non-capital purchases
1BGST credits on G10 + G11 purchases (input GST / 11)
W1Wages paid (gross)
W2PAYG withheld from wages
5APAYG instalment (income tax pre-payment)
Net(1A − 1B) + W2 + 5A = amount owed

If 1B > 1A (e.g. major fit-out month with large materials purchase), the builder is in a GST refund position for that quarter.

GST on progress claims

A progress claim of $110,000 (GST-inclusive) breaks down as:

  • $100,000 builder revenue.
  • $10,000 GST collected on behalf of ATO.

On cash basis, GST liability triggers when payment is received. If the client pays in Quarter 1, the $10,000 GST goes on the Q1 BAS due 28 October.

Common builder error: treating the $110,000 as $110,000 of builder cash. The $10,000 belongs to ATO. Sweep it to the tax account immediately.

GST on retention

Retention (typically 5% of contract value held back) creates a timing question.

ScenarioGST treatment
Retention held back from invoice (client invoiced $100k, paid $95k, $5k retention)GST on $100k invoice issued, but on cash basis, GST liability only on $95k received until retention paid
Retention released after defects periodGST on $5k released triggers when paid

A clean record-keeping system tracks retention separately so the right cash trigger fires the right GST entry.

Variations and GST

Variations are GST-bearing the same as the original contract:

  • Variation form quotes price GST-inclusive.
  • Variation invoice issued at next stage.
  • GST collected on variation payment.

Common error: variation work done but invoice never issued. The work happens, the GST never lands on a BAS. The ATO doesn’t care that the builder forgot to invoice; if they audit the project and reconcile claimed expenses against revenue, missing variation revenue is a red flag.

Trade and supplier invoices: claiming credits

Builder receives a trade invoice for $11,000 GST-inclusive:

  • $10,000 trade cost (expense).
  • $1,000 GST credit (reduces builder’s BAS liability).

Conditions for claiming GST credit:

  • Trade is GST-registered (their invoice will show “Tax Invoice” and an ABN).
  • The invoice is for a business purpose (any residential build work qualifies).
  • The builder has the tax invoice in their records.

For invoices < $82.50 (GST-inclusive), simplified records are acceptable (a receipt without an ABN).

Unregistered traders cannot charge GST. If a trade invoice for $11,000 doesn’t show an ABN or “Tax Invoice”, question it before paying GST on something the trade can’t pass to ATO.

ATO penalties for late lodgement

Late BAS lodgement triggers:

  • Failure to lodge on time (FTL) penalty: $312.50 per 28-day period overdue (small entity rate, 2026).
  • General Interest Charge (GIC): ~11.36% p.a. (2026 rate) on the outstanding amount.
  • DPN (Director Penalty Notice): if a company-structured builder fails to pay GST or PAYG, the company directors can be made personally liable.

Three lodgements late in 2 years can flag the builder for additional ATO compliance review.

The discipline

The single discipline that prevents most builder BAS trouble:

  1. A separate ATO-money savings account (the “tax account”).
  2. On every stage payment received, immediately sweep 1/11 (GST) plus the PAYG withheld portion into the tax account.
  3. At BAS lodgement, pay from the tax account.
  4. The operating account never touches GST or PAYG money.

A high-interest savings account (4-5% p.a. typical 2026) earns the float between collection and lodgement, partially offsetting the cost of cash sitting idle.

What about IAS (Instalment Activity Statement)?

Some builders also lodge IAS (typically monthly) for PAYG instalments on income tax. The IAS is essentially a sub-set of the BAS data. If quarterly BAS, no separate IAS. If monthly PAYG-only filer, the IAS is the monthly form.

For builders

  1. Confirm your GST basis (cash) at registration. Switch from accrual to cash if currently on accrual and cash matches your reality.
  2. Open a tax account (separate savings account at the same bank).
  3. Sweep on every stage payment receipt: 1/11 of the gross + PAYG withheld.
  4. Diary BAS due dates in your calendar with 14 days warning. 28 days isn’t much time when you’re chasing supplier invoices for credit claims.
  5. Engage a BAS agent if your books are messy. The extension to lodge ($300-$800 typical 2026 cost) often pays for itself in a single quarter.
  6. Reconcile BAS to bank statements every quarter. ATO automated checks compare your BAS data against bank reporting.

References

See also

Try it

(Chalkline app: BAS quarterly checklist generator. Coming soon.)

Last updated: 2026-05-15. Verified: 2026-05-15.

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