What is the penalty for a mistake on a BAS in Australia?

The ATO applies shortfall penalties starting at 25% of underpaid tax for failure to take reasonable care, increasing to 50% for recklessness. However, submitting an unprompted voluntary disclosure before the ATO notifies you of an audit generally reduces administrative penalties by up to 80% or waives them entirely. General Interest Charge (GIC) may still apply to late unpaid tax liabilities until the balance is cleared.

What is the difference between a BAS revision and a GST adjustment?

A BAS revision corrects an error that existed at the time of lodging, such as a missed expense, duplicate invoice, or clerical data entry mistake. A GST adjustment reflects a subsequent change in business circumstances after lodgement, including returned goods, cancelled contracts, bad debt write-offs, or changes in the creditable purpose of a purchased asset.

How far back can you amend a BAS with the ATO?

You can generally amend a Business Activity Statement up to four years from the day after the notice of assessment or the original statement due date. Under section 105-55 of Schedule 1 to the Taxation Administration Act 1953, the statutory entitlement period to claim uncredited GST input tax credits or overpaid tax strictly expires after four years.

What records must tradies keep when revising an activity statement?

Tradies must retain tax invoices, recipient-created tax invoices, adjustment notes, bank statements, and the original versus revised calculation worksheets for five years. Under section 382-5 of Schedule 1 to the Taxation Administration Act 1953, your records must clearly document the nature of the error, the date identified, and a complete audit trail from your accounting software.

What should I do if a BAS error affects PAYG withholding or payroll?

Payroll-related BAS errors cannot simply be corrected via standard GST net error rules; you must adjust the PAYG withholding labels by lodging a formal revision for the affected period. Discrepancies must also be reconciled against Single Touch Payroll (STP Phase 2) reports and superannuation guarantee records to ensure compliance with both the ATO and Fair Work regulations.

How do I amend a BAS after finding a GST mistake?

Amend an Australian BAS with a GST mistake by lodging a revision via ATO Online Services or correcting eligible errors under debit limits on your next BAS.

Quick answer

To amend a BAS after finding a GST mistake, lodge a revised activity statement through ATO Online Services or your registered tax agent. Businesses with turnover under $20 million may instead correct eligible debit errors under $12,500 on their next BAS within 18 months, while credit errors allow up to four years.

Skill level: General guidance
Time: Varies
Trade: Bookkeeping & Cashflow
Updated: 4 November 2026

Tools you will need

Xero Business Edition - Cloud Accounting & BAS Reconciliation Software
MYOB Business Pro - Trade Accounting & Activity Statement Software
Intuit QuickBooks Online - Small Business BAS Preparation Software
myGovID & Relationship Authorisation Manager (RAM) - ATO Online Services Portal
Microsoft Excel 365 - GST Calculation & Reconciliation Worksheet
Dext Prepare - Tax Invoice Capture & Audit Trail Tool

How do you amend an Australian BAS after finding a GST error?

If you find a GST mistake after lodging a business activity statement (BAS), you may need to revise the original BAS or correct the error on a later statement. The appropriate method depends on the type, value and age of the error, so acting promptly and keeping clear records is important.

What is the difference between a GST error and a GST adjustment on a BAS?

First determine whether the issue is a genuine GST error or a later GST adjustment. An error existed when the original BAS was lodged, while an adjustment generally arises because circumstances changed afterwards, such as a sale being cancelled or the price changing.

The ATO may allow eligible GST errors to be corrected on a later BAS, subject to its current time and value limits. If those conditions are not met, the earlier BAS will generally need to be revised.

A BAS revision replaces the relevant figures previously reported for that period. It can usually be requested through the ATO’s online services or lodged by a registered BAS agent.

Keep evidence showing what went wrong, how the corrected amount was calculated and which tax period it relates to. Supporting records may include tax invoices, credit notes, bank transactions, accounting reports and reconciliation workpapers.

Correcting an error can increase or reduce the amount payable. Interest or penalties may apply in some circumstances, although the ATO considers factors such as voluntary disclosure and reasonable care.

What ATO rules determine whether you can fix a GST mistake on a later BAS?

Whether the transaction was GST-free, input taxed, taxable or outside the GST system, and whether a valid tax invoice was required.

Whether the issue is an error in the original BAS, a later adjustment, a duplicate entry, an incorrect GST code or a timing difference.

The ATO’s current correction limits, review periods and eligibility rules for reporting the amount on a later BAS.

Whether the mistake affects other labels, including sales, purchases, PAYG withholding or instalments, rather than GST alone.

Whether the accounting file, bank reconciliations and GST control accounts agree with the revised figures and supporting documents.

Common Costly Mistakes

Automatically changing the next BAS without checking the ATO’s correction rules.

Editing or deleting old transactions without preserving an audit trail.

Claiming GST credits without valid supporting documents or in the wrong reporting period.

Correcting the GST label but failing to reconcile related sales, expense, debtor or creditor accounts.

When To Get Professional Help

DIY correction becomes risky when the error spans multiple periods, involves a material amount, affects GST classification or cannot be reconciled to the accounting records. A registered BAS agent can assess the appropriate correction method, prepare supporting workpapers and help communicate with the ATO without guaranteeing a particular compliance outcome.

Talk To A Specialist

If you are unsure whether to revise an earlier BAS or correct the amount later, consider arranging a bookkeeping health check. A specialist can review the records, identify any flow-on issues and explain the practical next steps: talk to a bookkeeping specialist.

Frequently Asked Questions

Can I fix a GST mistake on my next BAS?

Sometimes. The ATO allows certain eligible GST errors to be corrected on a later BAS, but time and value limits apply and differ depending on whether the correction increases or decreases the GST payable. Check the current ATO rules or ask a registered BAS agent before including the correction.

What is the difference between revising a BAS and making a GST adjustment?

A BAS revision generally corrects information that was wrong when the statement was originally lodged. A GST adjustment usually reflects a later change, such as a cancelled purchase, returned goods or a price change. The distinction affects how and when the amount should be reported.

What records should I keep when amending a BAS?

Keep the original and corrected calculations, relevant invoices or adjustment notes, transaction reports, bank records and an explanation of the error. The accounting file should retain a clear audit trail showing what changed, when it changed and which BAS period was affected.

Will the ATO charge penalties or interest for a BAS mistake?

It depends on the circumstances, including the nature of the error, the amount involved, whether reasonable care was taken and how quickly it was disclosed. Correcting an error voluntarily does not automatically remove interest or penalties, but prompt action and well-organised records can help the ATO assess the situation accurately.

What if the BAS mistake also affects payroll figures?

If PAYG withholding labels are wrong, the correction may also need to be checked against payroll reports and Single Touch Payroll records. STP and superannuation guarantee obligations are administered by the ATO, while wages and employee entitlements fall under Fair Work requirements, so payroll-related discrepancies should be reviewed carefully rather than treated as GST-only errors.

Important — General Information Only

This guide is general information only and is not personal bookkeeping & cashflow advice. It does not take into account your objectives, financial situation or needs. BAS correction rules and administrative limits can change, so consider your circumstances and check current ATO guidance before acting; for advice and BAS services, consult a registered BAS agent listed with the Tax Practitioners Board or another appropriately licensed or registered professional.

Frequently asked questions

Can I fix a GST mistake on my next BAS?: Yes, eligible GST errors can be corrected on your next activity statement if they meet Australian Taxation Office time and value limits. For businesses with an annual turnover under $20 million, net debit errors must not exceed $12,500 and must be corrected within 18 months of the original due date. Credit errors, where you overpaid GST or underclaimed input tax credits, can be corrected on a later BAS within four years without value restrictions.
What is the penalty for a mistake on a BAS in Australia?: The ATO applies shortfall penalties starting at 25% of underpaid tax for failure to take reasonable care, increasing to 50% for recklessness. However, submitting an unprompted voluntary disclosure before the ATO notifies you of an audit generally reduces administrative penalties by up to 80% or waives them entirely. General Interest Charge (GIC) may still apply to late unpaid tax liabilities until the balance is cleared.
What is the difference between a BAS revision and a GST adjustment?: A BAS revision corrects an error that existed at the time of lodging, such as a missed expense, duplicate invoice, or clerical data entry mistake. A GST adjustment reflects a subsequent change in business circumstances after lodgement, including returned goods, cancelled contracts, bad debt write-offs, or changes in the creditable purpose of a purchased asset.
How far back can you amend a BAS with the ATO?: You can generally amend a Business Activity Statement up to four years from the day after the notice of assessment or the original statement due date. Under section 105-55 of Schedule 1 to the Taxation Administration Act 1953, the statutory entitlement period to claim uncredited GST input tax credits or overpaid tax strictly expires after four years.
What records must tradies keep when revising an activity statement?: Tradies must retain tax invoices, recipient-created tax invoices, adjustment notes, bank statements, and the original versus revised calculation worksheets for five years. Under section 382-5 of Schedule 1 to the Taxation Administration Act 1953, your records must clearly document the nature of the error, the date identified, and a complete audit trail from your accounting software.
What should I do if a BAS error affects PAYG withholding or payroll?: Payroll-related BAS errors cannot simply be corrected via standard GST net error rules; you must adjust the PAYG withholding labels by lodging a formal revision for the affected period. Discrepancies must also be reconciled against Single Touch Payroll (STP Phase 2) reports and superannuation guarantee records to ensure compliance with both the ATO and Fair Work regulations.

Written by Tally, the Bookkeeping & Cashflow specialist at Aus.Tools.