Company Tax: What to Check Before You Trust the Number

Updated 30 August 2026 · Business and gst

A Company Tax Calculator gives a fast answer, but the answer is only as good as what goes in. These are the mistakes we see most often with company tax calculations in Australia, and how to avoid them.

1. Spending GST collected

GST belongs to the ATO. Keep it aside until your BAS is due.

2. Undercharging as a contractor

Your rate must cover super, leave, unbilled time and business costs, not just the salary you want.

3. Forgetting on-costs

An employee costs well above their salary once super, workers comp and payroll tax are included.

4. Mixing up margin and markup

A 50% markup is a 33% margin. Pricing with the wrong one can erase profit.

5. Overlooking the detail that matters most here

Base rate entities have turnover under $50 million and no more than 80% passive income.

How the company tax changes with company tax rate

A common mistake is getting one input slightly wrong. Here is what happens to the company tax when “Company tax rate (%)” is off by up to 20% in either direction, with everything else held steady.

Company tax rate (%)	Company tax
20	$40,000.00
22	$44,000.00
25	$50,000.00
28	$56,000.00
30	$60,000.00

At 20 the result is $40,000.00; at 30 it is $60,000.00. If a small change in this input moves the answer a lot, it is worth double-checking that figure before you rely on the result.

A quick sense check

Tax = taxable profit × rate (25% for base rate entities, 30% otherwise). With typical inputs the calculator returns company tax of $50,000.00. If your own result looks wildly different, check that each figure is in the right unit and period (weekly, monthly or yearly) before drawing conclusions.