Use Accounting Software to Do Your BAS: BAS and IAS Types Explained

Published May 19th, 2026 | Gimbla Contributor

Accounting software can make BAS preparation much easier, but it does not remove the need to understand which activity statement the ATO has issued. For an Australian small business, a BAS can report GST, PAYG withholding, PAYG instalments and other obligations. An instalment activity statement, or IAS, is usually narrower and is often used when GST is not being reported on that statement.

The practical workflow is simple: keep invoices, bills, bank transactions and payroll records up to date, reconcile them before the reporting period closes, then use your software to review the ATO activity statement labels before lodging or recording the payment. The tricky part is knowing whether you are looking at a BAS, an IAS, a GST instalment notice or a PAYG instalment notice.

BAS software works best when the records are already clean. The software can help calculate, prefill, lodge and record, but the business still needs to review what the ATO has asked for.

Quick answer

Use accounting software to do your BAS by keeping GST, payroll, purchases, sales and bank reconciliations current throughout the reporting period. When the ATO issues the activity statement, your software should help you review the relevant labels, such as GST collected, GST credits, PAYG withholding, PAYG instalments, fuel tax credits or other obligations that apply to your business.

According to the Australian Government’s BAS guidance, a BAS may be used to report GST, PAYG withholding, PAYG instalments, FBT instalments, luxury car tax and wine equalisation tax. Its PAYG instalments guidance also explains the key BAS versus IAS split: if you are registered for GST, PAYG instalments are reported on your BAS; if you are not registered for GST, they are reported on an IAS.

Key points

A BAS is personalised to your registrations, so not every business sees the same sections.
An IAS is not a mini-BAS for GST. It is commonly used for PAYG instalments, PAYG withholding or FBT instalments when GST is not being reported.
Instalment notices are simpler again: they may ask you to pay a prefilled GST or PAYG instalment amount without completing a full statement.
Accounting software helps most when invoices, bills, payroll, bank feeds and reconciliations are updated before the BAS period closes.
Direct BAS lodgment still needs correct ATO authorisation and review. Software reduces manual handling; it does not make tax judgement calls for every situation.

BAS, IAS and instalment notices in plain English

The ATO uses activity statements to collect different tax obligations during the year. Business owners often call all of them “the BAS”, but there are several statement types.

Statement type	What it usually means	Common obligations included	Who may see it
BAS	Business Activity Statement	GST, PAYG withholding, PAYG instalments, FBT instalments, fuel tax credits, WET or LCT where relevant	Businesses registered for GST or with several tax obligations
IAS	Instalment Activity Statement	PAYG instalments, PAYG withholding, FBT instalments, or similar non-GST obligations	Businesses or individuals not reporting GST on that statement
GST instalment notice	A prefilled notice for GST instalment reporting	GST instalment amount, often with limited fields	Businesses using the GST instalment method
PAYG instalment notice	A prefilled notice for income tax instalments	PAYG instalment amount	Businesses, sole traders, companies, trusts or investors in the PAYG instalment system
GST and PAYG instalment notice	A combined instalment notice	GST instalment amount and PAYG instalment amount	Businesses with both instalment obligations and simplified reporting for that period

The main thing is not the form name. The main thing is the obligation. If the statement asks for GST labels, you need sales, purchase and GST records. If it asks for PAYG withholding, you need payroll records. If it asks for a PAYG instalment, you need to understand whether it is a prepayment of income tax, not a normal business expense.

Common BAS types you may see in software

Inside ATO-connected software, BAS forms can appear as technical statement types. Most business owners do not need to memorise the codes, but they are useful when software, a BAS agent or an ATO message refers to them.

BAS type	Reporting period	Typical combination of obligations
BAS A	Quarterly	GST, PAYG instalments and PAYG withholding
BAS C	Quarterly	GST, WET, LCT, PAYG instalments, PAYG withholding and FBT instalments
BAS D	Quarterly	GST only
BAS F	Quarterly	GST and PAYG withholding
BAS U	Quarterly	GST, PAYG instalments, PAYG withholding and fuel tax credits
BAS V	Quarterly	GST, WET, LCT, PAYG instalments, PAYG withholding, FBT instalments and fuel tax credits
BAS W	Quarterly	GST and fuel tax credits
BAS X	Quarterly	GST, PAYG withholding and fuel tax credits
BAS G	Monthly	GST, WET, LCT, PAYG instalments and FBT instalments
BAS Y	Monthly	GST, WET, LCT, PAYG instalments, PAYG withholding, FBT instalments and fuel tax credits

These codes are software-facing shorthand. Your actual BAS will still be driven by your ATO registrations, reporting cycle and the labels issued for that period.

Common IAS and instalment notice types

IAS and instalment notices are more focused than a BAS. They usually exist because the ATO wants a specific instalment or withholding report without the full GST reporting section.

IAS or notice type	Reporting period	Typical combination of obligations
AS B	Quarterly	PAYG instalments only
AS I	Monthly or quarterly	PAYG withholding only
AS J	Quarterly	PAYG instalments, PAYG withholding and FBT instalments
Form N	Annual	PAYG instalment amount
Form R	Quarterly	PAYG instalment amount
Form S	Quarterly	GST instalment amount
Form T	Quarterly	GST instalment amount and PAYG instalment amount

If you receive an instalment notice with a prefilled amount, you may not need to complete a full activity statement unless you are varying the amount or the notice asks for extra information. If you are unsure, check the ATO notice or ask a registered tax or BAS agent.

How accounting software helps with BAS preparation

Accounting software is useful because it brings the BAS evidence into one place. Instead of rebuilding the quarter from bank statements and spreadsheets, you can review the records that already sit behind the BAS labels.

For GST, your software should help you check:

taxable sales and GST-free sales
GST collected on invoices and receipts
GST paid on supplier bills and expenses
adjustments, credit notes and refunds
transactions that have been coded to the wrong tax rate
whether the GST balance agrees with your balance sheet

For PAYG withholding, payroll software should help you review wages, withheld amounts and payroll reports. If you employ staff, your activity statement should agree with the payroll records you have used for pay runs and Single Touch Payroll reporting.

For PAYG instalments, the figure may be prefilled by the ATO. This is not the same as PAYG withholding. PAYG withholding is tax you withhold from people you pay. A PAYG instalment is a prepayment towards your own expected income tax on business or investment income.

A practical BAS software workflow

Use this workflow before you lodge or send figures to your accountant.

Reconcile every business bank account and credit card for the BAS period. Gimbla’s bank reconciliation guide is a good starting point.
Review sales invoices, receipts, credit notes and refunds. Make sure GST has been applied only where it should be.
Review supplier bills, expense claims and imported bank transactions. Check that private spending, GST-free purchases and non-capital purchases are not all being treated the same way.
If you employ staff, compare payroll reports with the PAYG withholding section of the activity statement.
Check any ATO prefilled PAYG instalment or GST instalment amount. Do not overwrite it casually; varying an instalment should be based on a reasonable estimate.
Run your GST or tax transactions report and compare it with your BAS or IAS labels.
Lodge through authorised software, online services or your registered agent.
Record the payment or refund against the correct liability or asset account so the balance sheet stays tidy.

In Gimbla, the GST, VAT and Sales Tax guide shows the basic tax clearing workflow after reporting. If PAYG instalments appear on your BAS or IAS, the PAYG instalment posting guide explains why those payments should be tracked separately from ordinary expenses.

What software cannot do for you

Software can help with calculations and lodgment, but it cannot decide every tax treatment by itself. A few areas still need human review:

whether the business should be registered for GST
whether a sale is taxable, GST-free, input taxed or outside scope
whether a purchase has a valid tax invoice
whether a worker is an employee or contractor
whether PAYG instalments should be varied
whether WET, LCT, fuel tax credits or FBT instalments apply
whether a prior BAS needs a correction or revision

This is where clean software records and professional advice work together. Good software makes the numbers visible. Your accountant, BAS agent or tax adviser can help with the judgement calls.

When Gimbla fits the BAS workflow

Gimbla is useful when you want your BAS work to sit close to the transactions that created it. Invoices, bills, bank reconciliations, payroll records, GST reports and BAS lodgment all connect back to the same accounting file.

For Australian businesses, Gimbla’s BAS lodgment workflow is designed to reduce the manual step of copying figures from your accounting software into the ATO portal. You can also follow the register software ID guide when you need to connect hosted software services with the ATO.

That does not mean you should skip review. It means the review starts from better records: reconciled bank accounts, consistent tax coding, clear payroll reports and a saved lodgment trail.

Frequently asked questions

Can accounting software lodge my BAS directly?

Some accounting software can lodge activity statements through ATO-connected Standard Business Reporting services. You still need the correct ATO authorisation, accurate business settings and a careful review before lodging.

Is an IAS the same as a BAS?

No. A BAS is generally used by businesses registered for GST and can include GST plus other obligations. An IAS is used for instalment or withholding obligations when GST is not being reported on that statement.

Why did I receive an instalment notice instead of a BAS?

If your only obligation for the period is an instalment amount, such as a PAYG instalment or GST instalment, the ATO may issue an instalment notice instead of a full activity statement. The notice may already show the amount to pay.

Can software decide which BAS labels apply to me?

Software can help populate the labels that match the statement issued by the ATO, but your registrations, reporting cycle and ATO prefill determine which sections apply. Treat the software as a workflow and review tool, not a substitute for checking your obligations.

Final thought

Using accounting software to do your BAS is not just about pressing lodge. It is about keeping records current enough that BAS time becomes a review process, not a scramble.

Start by identifying the statement type: BAS, IAS or instalment notice. Then match each label to the records behind it. Once the numbers are reconciled and reviewed, software can help you lodge, pay and keep a clean audit trail for next quarter.