Car Expense Deduction: What to Check Before You Trust the Number

Updated 19 June 2026 · Tax and pay

A Car Expense Deduction 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 car expense deduction calculations in Australia, and how to avoid them.

1. Forgetting the Medicare levy

Most take-home pay estimates that leave out the 2% levy overstate pay by hundreds or thousands of dollars.

2. Using last year’s tax rates

Brackets and offsets change. The Stage 3 changes from 1 July 2024 and further cuts from 1 July 2026 mean older figures can be well off.

3. Treating a deduction as a refund

A $1,000 deduction reduces taxable income by $1,000. The cash benefit is only your marginal rate on that amount.

4. Confusing marginal and average tax rates

Moving into a higher bracket only raises the tax on the dollars above that threshold. Your average rate is always lower than your marginal rate.

5. Overlooking the detail that matters most here

Trips between home and your usual workplace are private travel and cannot be claimed, even if you run errands on the way.

How the deduction changes with cents per kilometre

A common mistake is getting one input slightly wrong. Here is what happens to the deduction when “Cents per kilometre” is off by up to 20% in either direction, with everything else held steady.

Cents per kilometre	Deduction
70	$2,800.00
79	$3,160.00
88	$3,520.00
97	$3,880.00
106	$4,240.00

At 70 the result is $2,800.00; at 106 it is $4,240.00. 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

Deduction = work km (capped at 5,000) × the ATO rate per km (88 cents for 2024–25; check the current year). With typical inputs the calculator returns deduction of $3,520.00. 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.