BAS Preparation Guide

What a BAS actually is

A business activity statement is the ATO's consolidated reporting form. It's how you report and pay several obligations in one place — most commonly GST, PAYG withholding (the tax you've withheld from employee wages) and PAYG instalments (prepayments towards your own income tax). Some businesses also report fuel tax credits, luxury car tax or wine equalisation tax on the same form.

If you're registered for GST, you'll lodge a BAS. Your reporting cycle — monthly, quarterly or annually — depends on your turnover and circumstances; the ATO sets your cycle and publishes the current due dates for each period. Lodging through a registered agent typically gives you a later due date than lodging yourself, which is one of the quiet benefits of using one.

Cash versus accruals — the setting that shapes everything

GST can be accounted for on a cash basis (you report GST when money actually moves) or an accruals basis (you report when the invoice is issued or received). Cash accounting is generally kinder to small-business cashflow — you never remit GST on an invoice a customer hasn't paid. Accruals matches your GST reporting to your profit-and-loss view. Eligibility for cash accounting depends on turnover thresholds the ATO publishes. Whichever basis you're on, the critical thing is that your accounting software is set to the same basis — a mismatch here is a common source of BAS errors that compound quarter after quarter.

Preparing a BAS: a working method

A BAS should be the output of tidy books, not an archaeology project. A repeatable preparation routine looks like this:

• Reconcile bank accounts to the end of the period. Every transaction matched, no unreconciled lines. This is the foundation; skip it and every later number is provisional.
• Review GST coding on transactions. The recurring troublemakers: bank fees and interest (input-taxed), overseas software subscriptions (often no GST, or GST under different rules), insurance (the stamp duty component), motor vehicle purchases, and wages (no GST — a surprisingly common miscode).
• Check tax invoices exist for the larger purchases you're claiming credits on. The ATO requires valid tax invoices above a threshold it publishes.
• Reconcile PAYG withholding to your payroll reports for the period — the BAS figure should match what your STP filings have already told the ATO.
• Review the GST reports your software generates, compare against the same period last year, and investigate anything that looks out of pattern before lodging.
• Lodge and pay by the due date — or contact the ATO early if you can't pay, because payment plans are far easier to arrange before a deadline than after.

Common errors worth knowing by name

• Claiming GST credits on GST-free purchases — the software defaults a code and nobody checks it.
• Reporting gross wages in the GST section rather than only at the withholding labels.
• Missing the private-use adjustment on expenses that are partly personal.
• Double-counting income when payment platforms deposit net of fees and the fees never get recorded.
• Rushing corrections. Most modest errors can be corrected on a later BAS within limits the ATO sets — you rarely need to panic, but you do need to fix them.

Making BAS boring (in a good way)

The businesses that find BAS stressful are almost always the ones doing a quarter's worth of bookkeeping in the week it's due. The fix isn't heroics at the deadline — it's a weekly bookkeeping rhythm so period-end is a review, not a rebuild. That's the core argument in our guide to systemising your business: move the work upstream and the deadline stops being an event. If BAS preparation currently depends on one person's memory of how things are coded, that's a fragility worth fixing too — see our finance function overview for how a properly structured bookkeeping-to-BAS pipeline works.

One note on the rules themselves: BAS and GST are regulated territory, and the details above are general in nature — your BAS agent or accountant is the right person to confirm how they apply to your structure.