Car Logbook Method: The 12-Week Rule and 5-Year Validity

General information only. This is not tax or financial advice. Consult a registered tax agent for advice specific to your situation.

If you claim work-related car expenses using the logbook method, the ATO expects a specific record-keeping standard. Done properly, the logbook method can produce significantly larger deductions than the cents-per-kilometre method — but only if your records are compliant and your work-use percentage is well-documented.

How the logbook method works

The logbook method works in two steps:

1. Establish your business-use percentage by keeping a logbook for at least 12 continuous weeks.
2. Apply that percentage to your total car running costs for the full income year.

For every trip during the 12-week period, you must record:

• Date of the trip
• Start and end odometer readings
• Kilometres travelled
• Purpose of the trip (work or private)
• For work trips: the destination and reason (e.g. “client visit — Parramatta”)

At the end of the 12 weeks, divide your total work kilometres by your total kilometres to get your business-use percentage. That percentage is then applied to all your car running costs for the year — not just for those 12 weeks.

What counts as a running cost

The logbook method lets you claim a share of every genuine running cost for the car:

• Fuel — keep receipts or use a fuel app
• Registration — the full annual cost apportioned to work use
• Insurance — comprehensive and CTP premiums
• Servicing and repairs — log-books, tyres, brake pads, batteries
• Interest on a car loan — if you borrowed money to buy the car
• Depreciation — calculated under ATO effective life rules (8 years for most passenger cars, subject to the luxury car limit)
• Roadside assistance membership — e.g. NRMA, RACV, RAA

You cannot claim parking fines, speeding fines, or the cost of a car you don’t own.

The 12-week requirement in practice

The 12-week period must be continuous and representative of your normal annual driving pattern. The ATO can disallow your claim if the logbook period was cherry-picked to inflate your work-use percentage.

Practical tips for choosing your 12 weeks:

• Avoid school holiday periods if your normal work involves visiting multiple client sites — your pattern will look different when traffic is lighter.
• Include a typical mix of weeks — don’t start just before a period of unusually heavy work travel.
• Start at the beginning of a week so it’s easier to track.
• If you have irregular work travel (e.g. site visits some months, desk-only others), include a mix of both.

You do not need to keep the logbook every year. Once established, it is valid for five income years — as long as your work-use pattern doesn’t change materially.

When you must start a new logbook

You need a fresh 12-week logbook if:

• Your job changes and you drive more or less for work
• You change employers or roles and your travel pattern shifts
• You acquire a new car (a logbook is tied to a specific vehicle)
• More than five years have passed since the current logbook was kept

A change in the number of days you work from home can also affect your logbook if it changes how often you drive to client sites or a separate workplace.

Odometer records at year end

Even in years when you are not keeping an active logbook, you must record your odometer reading at 30 June each year. This allows the ATO (or your tax agent) to calculate total kilometres travelled in the year and apply the work-use percentage to actual running costs.

Worked example: logbook vs cents per kilometre

Rachel is a project manager who drives to client sites across the city. Here is how the two methods compare for her situation:

	Logbook method	Cents per km
Total km driven	25,000	25,000
Work km	14,000 (56%)	Capped at 5,000
Total car running costs	$12,000	—
Rate applied	$12,000 × 56%	5,000 × $0.88
Deduction	$6,720	$4,400

Rachel saves $2,320 in deductions by using the logbook method. At a 34.5% marginal tax rate (including Medicare levy), that is roughly $800 more in her pocket at tax time.

The logbook method is almost always better for drivers who travel more than 5,000 work kilometres per year, or who have a high-value car with significant depreciation and running costs.

Records you must keep

To satisfy the ATO, keep the following for each income year:

Record	Purpose
Logbook (12-week period)	Establishes business-use percentage
Odometer readings (start and end of year)	Calculates total km for the year
Fuel receipts	Running cost substantiation
Service invoices	Running cost substantiation
Insurance and registration documents	Running cost substantiation
Loan statements (if applicable)	Interest component calculation

The ATO recommends keeping records for five years after you lodge your return.

Common mistakes to avoid

• Logbook not continuous — gaps in the 12-week period can make it non-compliant.
• Period not representative — a logbook kept during an unusually busy travel month overstates your work-use percentage.
• Home-to-work travel included — ordinary commuting between home and your regular workplace is private travel and cannot be claimed.
• No year-end odometer reading — without this, your total kilometres for the year cannot be verified.
• Missing receipts — claiming fuel costs without receipts is a common audit trigger.

Key takeaways

• Keep a 12-week continuous logbook to establish your business-use percentage.
• Record every trip: date, odometer readings, kilometres, and purpose.
• Apply your work-use % to all car running costs for the full year — fuel, rego, insurance, servicing, depreciation, and loan interest.
• The logbook is valid for five years unless your usage changes significantly.
• Record your odometer reading at 30 June each year, even in non-logbook years.
• If you drive more than 5,000 work km/year or own a more expensive car, the logbook method will almost always produce a larger deduction than cents per kilometre.