Running a small business comes with enough challenges already.
The last thing you want is to lose money because of avoidable tax mistakes.
But every year, thousands of Australian businesses do exactly that.
They:
- overpay tax
- miss deductions
- get hit with penalties
- trigger ATO attention
And the frustrating part?
👉 Most of these mistakes are completely avoidable.
In 2026, with increased ATO data matching, tighter rules and changes like Payday Super, there’s less room for error than ever before.
This guide breaks down the most common small business tax mistakes — and shows you exactly how to avoid them.
Why Tax Mistakes Are More Costly in 2026
Things have changed.
The ATO is now:
- using real-time data
- cross-checking multiple systems
- identifying inconsistencies faster
- applying penalties more quickly
That means:
👉 mistakes are picked up sooner
👉 penalties happen faster
👉 audits are more targeted
This makes getting things right more important than ever.
Mistake #1 — Mixing Personal and Business Finances
This is one of the most common problems we see.
Business owners often:
- use one account for everything
- pay personal expenses from business funds
- don’t track transactions properly
Why this is a problem
It makes it difficult to:
- track deductions
- justify expenses
- prepare accurate BAS
- respond to ATO queries
How to fix it
- open a separate business bank account
- use a separate card for business expenses
- avoid transferring money randomly
Mistake #2 — Claiming Incorrect Deductions
Many businesses either:
- claim things they shouldn’t
- OR miss deductions they could claim
Examples of incorrect claims
- personal fuel
- groceries
- holidays labelled as business trips
- home expenses without clear use
Examples of missed deductions
- software subscriptions
- tools and equipment
- small asset purchases
- professional services
How to fix it
- only claim legitimate business expenses
- keep receipts
- get advice if unsure
Mistake #3 — Poor Record Keeping
If your records aren’t accurate, everything else falls apart.
Common issues include:
- missing receipts
- inconsistent records
- outdated bookkeeping
- relying on memory
Why this matters
If the ATO reviews your business:
👉 you must prove every claim
How to fix it
- use accounting software
- update records regularly
- store digital copies of receipts
Mistake #4 — Lodging BAS Incorrectly
BAS errors are a major trigger for ATO attention.
Common mistakes:
- incorrect GST claims
- missed lodgements
- inconsistent reporting
How to fix it
- reconcile accounts monthly
- double-check GST treatment
- use a bookkeeper or accountant
Mistake #5 — Late Superannuation Payments
Super is one of the strictest areas.
If you miss deadlines:
- penalties apply
- interest is charged
- payments are NOT deductible
With Payday Super coming in 2026
This becomes even more important.
How to fix it
- pay super on time
- align payments with payroll
- prepare for real-time super
Mistake #6 — Ignoring ATO Debt
Some businesses:
- ignore tax bills
- delay payments
- hope it resolves itself
It doesn’t.
Why this is worse in 2026
ATO interest is now:
👉 not tax deductible
How to fix it
- act early
- set up a payment plan
- speak to your accountant
Mistake #7 — Not Planning for EOFY
Waiting until June is too late.
By then:
- opportunities are gone
- decisions are rushed
- mistakes happen
How to fix it
- start planning in April
- review your position early
- act before deadlines
Mistake #8 — Not Using the Instant Asset Write-Off Properly
Some businesses:
- don’t use it at all
- misuse it
- buy assets they don’t need
How to fix it
- only buy what makes sense
- ensure assets are installed before 30 June
- understand the rules
Mistake #9 — Poor Cash Flow Management
Tax problems often start with cash flow problems.
If you don’t manage cash flow:
- you fall behind on tax
- you miss payments
- you rely on debt
How to fix it
- track income and expenses
- forecast cash flow
- improve invoicing
Mistake #10 — Trying to Do Everything Yourself
Many business owners try to:
- manage bookkeeping
- handle tax
- interpret ATO rules
This often leads to mistakes.
How to fix it
- get professional support
- use systems
- focus on running your business
What Happens If You Get It Wrong
The consequences can include:
- penalties
- interest charges
- audits
- back payments
- stress
- lost time
In serious cases, it can escalate further.
How to Stay Compliant in 2026
Keep it simple:
- keep accurate records
- separate finances
- pay super on time
- lodge BAS correctly
- plan before EOFY
- get advice early
How Carmody Accounting Helps You Avoid These Mistakes
At Carmody Accounting, we work with small businesses across Penrith and Western Sydney to keep things simple and compliant.
We help you:
- avoid common tax mistakes
- identify deductions
- stay ahead of ATO changes
- manage BAS and GST
- improve cash flow
- plan for EOFY
- reduce stress
FAQ
What is the most common tax mistake for small businesses?
Mixing personal and business finances and poor record keeping.
How can I avoid ATO penalties?
Keep accurate records, lodge on time and pay super correctly.
Do I need an accountant for a small business?
While not required, having an accountant significantly reduces risk and improves tax outcomes.