What Are BAS and IAS? Key Differences, Preparation and Lodgement
Receiving a BAS or IAS can be confusing if you are unsure why the Australian Taxation Office has issued it or what you need to report.
BAS and IAS are both activity statements used to report business tax obligations. A Business Activity Statement includes GST reporting, while an Instalment Activity Statement does not. Depending on your registrations and reporting cycle, either statement may also include PAYG instalments, PAYG withholding or other assigned obligations.
A GST-registered employer may report GST through a quarterly BAS while receiving an IAS for PAYG withholding between quarters. The ATO determines which statements your business receives based on its reporting requirements.
Here, IAS means Instalment Activity Statement, not International Accounting Standards. This guide explains the differences, why a business may receive one or both, what records are needed and how preparation and lodgement work.
What Is the Difference Between BAS and IAS?
A Business Activity Statement includes GST reporting, while an Instalment Activity Statement does not. Both may also report obligations such as PAYG instalments, PAYG withholding or FBT instalments. A business can receive both when its GST and other tax obligations follow different reporting cycles.
| Comparison point | BAS | IAS |
| Full name | Business Activity Statement | Instalment Activity Statement |
| GST reporting | Includes GST reporting where applicable | Does not include GST reporting |
| Other obligations | May include PAYG withholding, PAYG instalments, FBT instalments and other assigned labels | May include PAYG withholding, PAYG instalments or FBT instalments |
| Who may receive it | Commonly issued to GST-registered businesses | Issued where relevant obligations are not being reported through a BAS for that period |
| Can a business receive both? | Yes | Yes |
The ATO issues each statement according to the business’s registrations and reporting requirements. The practical question is not simply whether the business is registered for GST, but which obligations must be reported and how frequently they are due.
What Is a Business Activity Statement?
Business activity statement – front
Business activity statement – rear
A Business Activity Statement is an ATO form used to report business tax obligations for a specific reporting period. GST-registered businesses generally use a BAS to report GST collected on sales and eligible GST credits on business purchases.
Depending on the business’s registrations and reporting requirements, a BAS may also include:
- PAYG withholding from employee wages or other payments
- PAYG income tax instalments
- Fringe Benefits Tax instalments
- fuel tax credits
- other tax labels assigned by the ATO
Not every BAS contains all of these sections. The ATO issues the statement with the labels relevant to the business, so the information required can differ between entities and reporting periods.
Before preparing a BAS, the accounting records should be reconciled and the GST treatment of transactions checked. A software-generated report can organise the figures, but it should still be reviewed against bank records, invoices, payroll reports and the labels shown on the statement.
The ATO provides further guidance on Business Activity Statements, including the obligations that may be reported through a BAS.
What Is an Instalment Activity Statement?
Instalment activity statement – front Instalment activity statement – rear
An Instalment Activity Statement is an ATO form used to report tax obligations that do not include GST. In Australian accounting, IAS commonly refers to this statement rather than International Accounting Standards.
An IAS is not a separate tax. It may be used to report or pay:
- PAYG income tax instalments
- PAYG withholding from employee wages or other payments
- Fringe Benefits Tax instalments
The exact labels depend on the obligations assigned by the ATO. Some taxpayers may receive an IAS containing only a PAYG instalment, while others may need to report PAYG withholding or another relevant amount.
IAS is sometimes described as a form only for businesses that are not registered for GST, but that explanation is incomplete. A GST-registered business may also receive an IAS when one of its obligations is reported more frequently than GST.
PAYG instalments and PAYG withholding serve different purposes. PAYG instalments are prepayments towards expected income tax, while PAYG withholding is tax withheld from payments such as employee wages and remitted to the ATO.
Why Might a Business Receive BAS, IAS or Both?
The ATO determines which activity statements a business receives based on its registrations, tax obligations and reporting cycles. A business may receive only BAS, only IAS or both during the same quarter because different obligations can be reported at different frequencies.
GST-Registered Business Reporting Everything Quarterly
A smaller GST-registered business may report GST, PAYG withholding and PAYG instalments together through one quarterly BAS. It may not receive a separate IAS because its activity-statement obligations follow the same quarterly cycle.
GST-Registered Employer Reporting PAYG Monthly
A GST-registered employer may report GST quarterly but PAYG withholding monthly. It could receive an IAS in the first two months of the quarter, followed by a BAS at quarter-end that includes GST and the relevant PAYG withholding amount for that month.
This is one common reason a business receives both forms. They cover different obligations or reporting periods rather than charging the business twice for the same liability.
Non-GST-Registered Business Paying PAYG Instalments
A sole trader or entity that is not registered for GST may receive an IAS for PAYG income tax instalments. The ATO may calculate an instalment amount or rate using information from an earlier tax return, and our self-employed tax guide explains how these instalments fit alongside income tax, GST, deductions and record-keeping obligations.
Not every non-GST-registered business receives an IAS. These examples are general, and the forms and reporting cycles that apply depend on the registrations and obligations recorded by the ATO.
What Information Is Needed to Prepare BAS or IAS?
Preparing BAS or IAS starts with complete, reconciled records for the reporting period. The exact information required depends on the labels shown on the activity statement, but common records include:
- sales and other business income
- purchases and operating expenses
- GST collected and eligible GST credits
- tax invoices and supporting documents
- reconciled bank and credit-card accounts
- payroll reports and PAYG withholding totals
- PAYG instalment amounts pre-filled by the ATO
- asset purchases or disposals
- fuel tax credit information, where relevant
- adjustments or errors carried over from an earlier period
Not every item applies to every business. An IAS containing only a PAYG instalment requires different information from a BAS that includes GST, payroll and other reporting obligations.
The records should also agree. For example, the PAYG withholding total in payroll software should match the relevant general-ledger accounts. Accounting software can organise transactions and generate reports, but unreconciled transactions, incorrect coding and private expenses can still affect the result.
Where bookkeeping is incomplete or frequently corrected at BAS time, an ongoing outsourced bookkeeping service may help maintain cleaner records throughout the reporting period.
How Are BAS and IAS Prepared and Lodged?
Preparing and lodging BAS or IAS involves more than transferring figures from accounting software into an ATO form. A typical process is:
- Identify the statement issued. Check whether the ATO has issued a BAS or IAS and which obligations appear on it.
- Confirm the reporting period and due date. Make sure the records cover the correct month, quarter or other assigned period.
- Reconcile the relevant records. Review bank accounts, credit cards, sales, expenses, payroll and other information connected with the statement.
- Check ATO-pre-filled amounts. Review any PAYG instalment information already shown on the statement.
- Complete the relevant labels. Enter the figures required for the obligations shown.
- Review the completed statement. Compare totals with the accounting and payroll records and investigate unexpected differences.
- Lodge through an available ATO channel. Sole traders can generally use ATO online services linked to myGov. Other entities can use Online services for business, while registered tax and BAS agents can lodge through their professional systems.
- Pay any resulting liability. Lodgement and payment are separate obligations. A business should still address lodgement by the due date if it needs to discuss payment difficulty separately.
The ATO provides instructions on how to lodge an activity statement online. The exact process depends on the labels included on the statement. Businesses should not vary PAYG instalments or change reported amounts without understanding how the relevant rules apply.
When Are BAS and IAS Due?
BAS and IAS due dates depend on the reporting cycle assigned by the ATO, the statement issued and how it is lodged. The date shown on the statement or in the business’s ATO account should be checked before relying on a general deadline.
Monthly activity statements are generally due on the 21st day of the following month. Standard quarterly BAS due dates are generally:
- 28 October for the July to September quarter
- 28 February for the October to December quarter
- 28 April for the January to March quarter
- 28 July for the April to June quarter
Eligible businesses lodging electronically or through a registered agent may receive a later date in some circumstances. These concessions are not automatic, and some GST or PAYG obligations may follow other arrangements. Lodging the statement and paying the resulting amount are separate obligations, even where they share the same deadline.
Because dates and concessions can change, confirm the current BAS lodgement due dates before acting.
Common BAS and IAS Mistakes to Check Before Lodging
Accounting software can produce an activity-statement report quickly, but the report is only as reliable as the records behind it. Common issues include:
- Leaving accounts unreconciled: Missing, duplicated or incorrectly matched bank and credit-card transactions can affect the figures reported.
- Using the wrong GST code: Purchases may be treated as GST-inclusive when no GST applies, while taxable sales may be coded incorrectly.
- Claiming GST credits without adequate records: A transaction appearing in the accounting file does not automatically establish eligibility. Supporting tax invoices and the relevant requirements still matter.
- Reporting inconsistent payroll figures: PAYG withholding in payroll software should agree with the relevant general-ledger accounts and payment records.
- Overlooking ATO-pre-filled amounts: PAYG instalment amounts or rates shown on the statement should be reviewed rather than automatically replaced.
- Including private transactions: Personal purchases or drawings should not be treated as ordinary business expenses without review.
- Lodging before the bookkeeping is complete: Unentered invoices, uncoded transactions and unresolved reconciliation differences can make the report inaccurate.
- Confusing lodgement with payment: Submitting the statement does not pay the amount due. Payment must also be arranged using the correct reference details.
We often see discrepancies emerge when payroll reports, bank records and the general ledger are reviewed together. Resolving them before lodgement is usually simpler than investigating them after figures have been submitted.
Repeated inconsistencies or unsupported claims may also increase compliance risk or lead to further ATO questions. Our guide to common ATO audit triggers explains the broader issues that may increase review risk.
What If a Previous BAS or IAS Is Incorrect?
An incorrect BAS or IAS can usually be corrected, but the method depends on the type of error, when it occurred and whether the ATO’s conditions for correcting it on a later statement are met.
Some GST errors may be corrected on a later BAS where the relevant time and value limits are satisfied. If an error is not eligible for that treatment, the original activity statement may need to be revised.
For example, if a purchase was incorrectly coded as including GST, the business should identify when the error occurred, confirm its value and determine which correction method the ATO permits. The underlying accounting records should also be updated, with invoices, reconciliation reports and notes retained to support the adjustment.
Errors involving PAYG withholding, PAYG instalments or other labels may follow different requirements. Grow Advisory Group can review earlier lodgements and investigate discrepancies, but the appropriate treatment and ATO response will depend on the facts and applicable rules.
Can You Prepare and Lodge BAS or IAS Yourself?
Yes, businesses can generally prepare and lodge their own BAS or IAS. The business remains responsible for complete records, accurate figures and lodgement by the applicable due date.
Self-lodgement may be manageable where the obligations are straightforward, bookkeeping is current and reconciled, GST coding is reliable, payroll reports agree with the accounts and no earlier errors remain unresolved.
Sole traders can generally lodge through ATO online services linked to myGov. Other entities can use Online services for business or compatible Standard Business Reporting software.
Professional support may be useful where records are incomplete, GST treatment is uncertain, payroll figures do not agree with the accounting file, several entities are involved or earlier statements may be incorrect. The decision should depend on the complexity and quality of the records rather than an assumption that every business must use an accountant.
How Grow Advisory Group Supports BAS and IAS Lodgement
Grow Advisory Group helps businesses prepare, review and lodge BAS and IAS using the accounting, payroll and transaction records available for the reporting period.
Our support may include reviewing reconciliations, checking GST coding, comparing payroll reports with PAYG withholding figures and reviewing the relevant activity-statement labels before lodgement. Where discrepancies appear, our team can help investigate the records and identify gaps in bookkeeping, payroll processes or account reconciliations.
We can also review earlier lodgements and help determine whether an issue may be corrected on a later statement or requires revision of the original activity statement.
Our accounting compliance and reporting services are available to small and medium businesses across the Gold Coast and Tweed Heads. The assistance required will depend on the records, the obligations shown and whether earlier reporting issues need to be resolved. Professional support does not guarantee a particular ATO outcome.
Frequently Asked Questions
Do You Need Help Preparing or Lodging an Activity Statement?
BAS and IAS do not report exactly the same obligations, and the statement your business receives depends on its registrations, reporting cycle and other tax requirements.
Before lodging, check that the statement covers the correct period and that accounting, payroll and banking records have been reconciled. Unresolved differences, incomplete bookkeeping or uncertainty about GST and PAYG figures should be addressed before submission.
Professional support may be useful where the records are complex, a previous statement may contain an error or the business receives BAS and IAS on different reporting cycles. Grow Advisory Group assists businesses across the Gold Coast and Tweed Heads with preparation, review, lodgement and corrections.
If you are unsure whether your records are ready or which figures should be reported, speak with our accounting team before the applicable lodgement deadline.
General information disclaimer: This article provides general information only and does not constitute personal tax, legal or financial advice. Activity statement requirements depend on your registrations, reporting cycle and circumstances.