You have found an error in a lodged BAS, or your accountant has, and the bookkeeper who made it is now either very quiet or suddenly an expert in why Xero did it. Before that turns into a spiral, here is what actually happens next: how the correction works, who is on the hook for any penalty, and how to have the conversation without letting it slide or blowing up the relationship over a one-off.

Published: July 2026

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First, know that most BAS errors are fixable

A mistake on a lodged BAS is not a catastrophe. The system expects errors and has a process for them. One useful distinction up front: a mistake is a number that was wrong at the time of lodgement, while an adjustment covers something that was right at the time but changed later, like a cancelled sale. For genuine mistakes, depending on the size and type, you either correct it on a later activity statement or lodge a revision of the original, and there is generally a four-year window to amend an activity statement, with a matching four-year time limit on claiming credits. You are not locked into a wrong number forever, and the goal is to fix it promptly and correctly, not to panic.

Say a Marrickville roastery discovers $4,300 of GST credits claimed across the year on overseas software subscriptions that never contained GST in the first place, week one homework for any new Marrickville bookkeeper taking over a file. That is a debit error, and in most cases one that size gets corrected on a later activity statement rather than by reopening the original, subject to the ATO's value and time limits. The mechanics of which path applies are a job for whoever manages your lodgements, and getting them right without drama is exactly what proper BAS lodgement is for. What you need to understand as the owner is the next two questions: who pays, and whether to stay.

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Who wears the penalty?

This is the question everyone actually wants answered, so here is the uncomfortable starting point: you, the taxpayer, remain liable for the correct amount of tax. If the error meant you underpaid GST, that GST was always owed, and it is still owed. A bookkeeper's mistake does not make a genuine tax liability disappear, and interest can still run on the shortfall until it is fixed, although remission can be requested.

Penalties are a different story. Where an error or a late lodgement was caused by a registered agent's failure, the safe harbour provisions can protect you from the administrative penalty, but only if the boxes are ticked. You must have engaged a registered tax or BAS agent. You must have given them all the relevant information in time for the lodgement to be done correctly, and the burden of proof on that point sits with you, not the ATO. And the agent's failure must have been a lapse in reasonable care rather than recklessness or intentional disregard, which safe harbour does not cover. The ATO assesses it case by case, and your agent is given the chance to respond to your version of events, which is why the email trail matters more than the argument.

Two things follow from that. First, safe harbour shields the penalty, never the underlying tax. Second, it only exists inside the registration system: a bookkeeper operating as an unregistered preparer cannot offer you this protection at all, which is one of the most concrete reasons to use a bookkeeper who lodges through a registered BAS agent rather than a cowboy with a login. Because outcomes turn on the specifics, this is a real "confirm with the ATO or a registered agent" situation, not something to resolve off a blog. But the principle is worth holding: the tax is yours, the penalty for a registered agent's error may not be.

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The conversation to have

Once you know a mistake happened, keep it factual, structured, and in writing. Three things, in order:

1. The facts. What was the error, which period, how big, and how was it found? Ask for it in an email, not a phone call. If safe harbour ever matters, evidence is the whole game.
2. The fix. What is the correction, will it go on the next activity statement or as a revision of the original, when will it be lodged, and what does it change about what you owe?
3. Who pays what. Is there a penalty or interest, who is bearing it, and is a remission or safe harbour request being made on your behalf? A professional who made the error should be running the correction at their cost and driving that process, not billing you to fix their own mistake.

How they respond tells you almost everything. A good bookkeeper owns it, fixes it fast, and is straight about the consequences. Barry gets defensive, blames the software, or goes quiet for eleven days. One of those is a professional having a bad day. The other is a pattern wearing a lanyard.

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One mistake or a pattern?

The real decision is never about a single error. Everyone makes one. It is about whether this is a one-off from someone whose work is otherwise solid, or the newest item in a series. Barry's version of accountability is a 400-word email about MYOB's servers and an invoice for the time it took to write it. If the BAS error is sitting on top of the signs your bookkeeper is ripping you off, or a habit of ghosting between quarters, the mistake is the symptom, not the disease. A Free Xero Roast will tell you whether the error was isolated or whether the whole file is shaky underneath, and how to change Sydney bookkeepers covers the exit cleanly if it is the latter.

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What to do this week

1. Get the error in writing: what it was, which period, how big, and how it was found.
2. Check your bookkeeper on the TPB's public register (free, takes two minutes). Registration determines whether safe harbour is even on the table.
3. Dig out the email trail showing you provided the information on time. Safe harbour runs on evidence, and the burden of proof is yours.
4. Confirm the correction path in writing: fixed on the next activity statement or a revision of the original, and what it changes about what you owe and when.
5. Skim the last four lodged periods against your reports. One error owned and fixed fast is human. Three found by your accountant is a diagnosis.

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Numbers worth knowing

• There is generally a four-year window to amend or revise an activity statement, and a four-year time limit on claiming GST and fuel tax credits. After that, unclaimed credits are simply gone.
• A late lodgement costs $330 for every 28 days overdue, capped at $1,650 for small entities, and doubles once turnover passes $1 million. Safe harbour can lift this off you when a registered agent caused the delay and you gave them everything in time.
• Interest on unpaid tax compounds daily at close to 11% a year and has not been tax deductible since 1 July 2025. Safe harbour covers penalties, not the tax, and not automatically the interest.

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Operator takeaway

If this page described your last quarter, do not schedule a "someday" cleanup. Book a Free Xero Roast this week, or book a chat with the number of open periods and your payroll frequency written down. Accountability for errors, at the bookkeeper's cost, is part of what a fixed monthly fee on The Packs is supposed to buy you, and clarity arrives a lot faster than motivation.

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FAQ

Can a BAS mistake be corrected after lodgement?

Yes. Depending on the type and size of the error, you either correct it on a later activity statement or lodge a revision of the original. There is generally a four-year window to amend an activity statement, and a four-year time limit applies to claiming credits.

If my bookkeeper made the mistake, do I still owe the tax?

Yes. You remain liable for the correct amount of tax regardless of who made the error, and interest can run on any shortfall until it is corrected. A mistake changes who might wear a penalty, not whether a genuine tax debt exists.

Who pays the penalty for a bookkeeper's BAS error?

Where a registered agent's failure caused the penalty, you gave the agent all relevant information in time, and the failure was not reckless or deliberate, the safe harbour provisions may protect you from the penalty. It never removes the underlying tax. Confirm your specific situation with the ATO or a registered agent.

Does safe harbour apply automatically?

No. The ATO assesses it case by case, you carry the burden of proving you provided the right information in time, and your agent is given the opportunity to respond to your claim. Keep everything in writing from the moment an error surfaces.

Why does it matter if my bookkeeper is a registered agent?

Safe harbour only applies to failures by a registered tax or BAS agent. An unregistered preparer cannot offer you that protection at all, no matter how the engagement is worded, which is one very practical reason to use a bookkeeper who lodges through a registered BAS agent.

How do I check if my bookkeeper is registered?

Search the Tax Practitioners Board's public register at tpb.gov.au. It is free, takes about two minutes, and shows the registration status and any conditions. If they are not on it, they are not registered, whatever the email signature says.

Should I fire my bookkeeper over one BAS mistake?

Not necessarily. A single error, owned and fixed quickly at their cost, is human. The decision should turn on whether it is isolated or part of a pattern of lateness, defensiveness and poor communication.

What should my bookkeeper do after making a BAS error?

Own it, confirm the correction path, lodge the fix promptly, be straight about any penalty or interest, and pursue remission or safe harbour on your behalf where relevant, at their cost rather than yours. Defensiveness, blame-shifting or silence is a bad sign.

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About Sydney Bookkeeper

Sydney Bookkeeper is the modern, fixed-price Sydney bookkeeper for businesses with staff that are tired of slow, hourly, jargon-spouting incumbents. We work with professional services firms, construction and property businesses, agencies, tech and ecommerce companies, hospitality groups, and health practices across Sydney. Monthly bookkeeping, BAS lodgement, payroll, and Xero file cleanups, all on fixed monthly pricing, no lock-in.

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The team uses a registered BAS Agent for all BAS and IAS lodgement services. Full registration details, agent particulars, and copies of the Tax Practitioners Board (TPB) Code of Professional Conduct, the TPB complaints process, and any conditions on the agent's registration are available on request. This content is general information only, written for Australian small and mid-market businesses. It does not constitute tax, financial product, or legal advice and should not be relied on as such. Penalty, amendment and safe harbour outcomes depend on your individual circumstances. For advice specific to your business, contact the team directly or consult a registered tax agent or the ATO. Sydney Bookkeeper is not a licensed tax agent or licensed financial adviser. Information was current at the time of publication and may change without notice. We review and update guides periodically.

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Sources

• Australian Taxation Office, Fixing BAS mistakes or making adjustments: https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/business-activity-statements-bas/fixing-bas-mistakes-or-making-adjustments
• Australian Taxation Office, Correct an activity statement: https://www.ato.gov.au/businesses-and-organisations/preparing-lodging-and-paying/fix-a-mistake-or-amend-your-tax-return/correct-an-activity-statement
• Australian Taxation Office, Penalties for making false or misleading statements: https://www.ato.gov.au/individuals-and-families/paying-the-ato/interest-and-penalties/penalties/penalties-for-making-false-or-misleading-statements
• Australian Taxation Office, Failure to lodge on time penalty: https://www.ato.gov.au/individuals-and-families/paying-the-ato/interest-and-penalties/penalties/failure-to-lodge-on-time-penalty
• Tax Practitioners Board, Safe harbour: https://www.tpb.gov.au/safe-harbour
• Tax Practitioners Board, Risks of using unregistered preparers: https://www.tpb.gov.au/risks-using-unregistered-preparers

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