BAS for Trades: Why Your BAS Keeps Biting You

You've had a good quarter. The jobs came in, the invoices went out, the bank account looked healthy for once. Then the BAS lands and suddenly you're staring at a number you didn't see coming and wondering where on earth it's going to come from.

If that's you, you're in very good company. It's the most common conversation in bookkeeping for tradies and the fix almost never involves working harder or charging more.

The money was never yours

Ouch! Sorry....Here's the uncomfortable bit. When you invoice a customer $11,000, you didn't earn $11,000. You earned $10,000 and collected $1,000 of GST on the ATO's behalf (we aren't opening up the can of worms breaking down that $10,000 in this post!).

That GST sat in your account for up to three months. It paid for materials. It covered a slow week. It bought the new trailer. By the time the BAS is due, it's gone and you're paying it out of this quarter's money instead.

Do that once and you catch up. Do it for three quarters running and you're permanently one BAS behind, funding old tax bills with new income. That's the trap, and it's a cash flow problem long before it's a tax problem.

Add PAYG withholding if you've got staff, and PAYG instalments once the ATO decides you're profitable enough to prepay next year's tax, and a quarterly BAS can quietly become the biggest single bill your business pays.

Why it feels like an ambush

Three things make it worse for trades businesses specifically:

Your income is lumpy. A big commercial job settles in one month, then you've got six weeks of small domestic work. The BAS doesn't care. It falls on the same date whether you've just been paid or you're still chasing a retention.

You get paid after you spend. Materials and subbies go out the door in week one. The customer pays in week nine...if you're lucky. GST is generally reported when you invoice, not when you're paid, unless you're on cash accounting. Plenty of businesses owe GST on money that hasn't landed yet.

Nobody's watching the number until it's due. If the books get done in a panic the week before lodgement, the first time anyone sees the figure is the day it has to be paid. There's no time left to do anything about it (I personally hate bookkeeping this way!).

Super changed the game in July

One more thing worth knowing if you employ anyone. From 1 July 2026, Payday Super means superannuation has to reach your employees' funds at the same time as their wages, not quarterly, the way it used to be.

For a lot of employers that quarterly super bill was doing double duty as an interest-free overdraft. That's gone. Super now leaves the account every pay run, which means your working capital genuinely changed shape this year. If your cash still feels tighter than the jobs board suggests it should, that's a big part of why.

ATO interest isn't what it used to be either

If you can't pay on time, a payment plan is still far better than silence, the ATO is much easier to deal with before a debt goes bad than after.

Sitting on a tax debt is a more expensive habit than it was two years ago because the interest continues to accrue on top of your balance owed every.single.month.

What actually fixes it

None of this is complicated. It just has to happen consistently.

Open a second bank account (at minimum!) and treat it like it's not yours. Every time money lands, move roughly 10% for GST, plus PAYG withholding and super if you've got staff. Some businesses set it at 25–30% of every deposit and never think about it again. When the BAS arrives, the money is already sitting there. That one habit removes the shock entirely.

Reconcile monthly, not quarterly. If your books are current, you know your GST position four to six weeks before it's due. That's enough time to chase a debtor, delay a purchase, or arrange a plan. Knowing early is most of the battle. I know a bookkeeper if you need one that will stay on top of your accounts weekly so you always have a real-time view.

Get your coding right. GST-free items, wages, bank fees and ATO payments all get treated differently. Coding errors flow straight into your BAS figure and into the amended return that follows.

Use the extra time you're entitled to. Lodging through a registered BAS agent generally gives you a later due date than lodging yourself for the September quarter, 25 November instead of 28 October. That's an extra four weeks of cash flow, every quarter, for doing nothing differently.

BAS for trades: what actually fixes it

A BAS shouldn't be a surprise. It should be a number you've watched building all quarter, in an account you've already put the money into.

That's the whole job, really. Not just lodging on time (though we do that), but making sure you know what's coming before it arrives, so the ATO becomes a scheduled cost like any other, instead of something that ambushes you four times a year.

If your BAS keeps biting you in the ...., it's worth a conversation!

Remote One Assist provides bookkeeping, BAS lodgement, payroll and compliance support to trades and service businesses across Australia.