If you use your car for work or business, chances are your log book is doing a lot of heavy lifting at tax time. But many people aren’t quite sure how long a log book lasts, or when it needs to be updated or replaced. The rules can feel a bit technical, and it’s easy to assume that once you’ve done a log book, you’re set forever. Unfortunately, that’s not always the case.
In this article, we break down when a log book is still valid, when you’ll need to start a new one, and the common situations that can catch people out. A quick check now can help you stay compliant — and avoid losing valuable deductions later.
How long does a log book last?
Under the tax rules, a properly completed 12‑week log book doesn’t just apply for one year. Once it’s done correctly, it’s generally valid for five income years — the year you prepare it, plus the next four years. This effectively puts log books on a five‑year cycle.
For example, if you prepared a log book during the 2020–21 income year, it would usually cover your claims from 2020–21 through to 2024–25. When you start preparing your 2025–26 tax return, that’s your cue to check whether the log book has expired. If it has, you’ll need to start a fresh 12‑week log to keep claiming car expenses.
When do you need to start a new log book?
There are a few common situations where a new log book is required. Some are obvious, others can catch people out.
Using the log‑book method for the first time
If you’re switching to the log‑book method for a vehicle and haven’t done one before, you’ll need to complete a new 12‑week log book. There’s no way around this — the ATO needs a proper starting point.
Adding another vehicle
If you start using an additional car for work or business purposes and want to claim using the log‑book method, each vehicle needs its own log book. You can’t reuse an existing one.
Replacing your vehicle
This is a big one. If you replace a car and don’t formally nominate the replacement vehicle in writing before lodging your tax return, your old log book won’t automatically carry over. In that case, you’ll need to start a new one.
If the replacement is nominated correctly and on time, the existing log book can continue to apply — but if that step is missed, a new log book is required.
When the ATO tells you to
In some cases, the Commissioner of Taxation may issue a notice requiring you to complete a new log book. If that happens, you’ll need to comply, regardless of how old your current log book is.
Lost or destroyed records
While the ATO does allow limited relief if records are lost or destroyed, this isn’t guaranteed and can be difficult to rely on. From a practical and compliance perspective, starting a fresh log book is usually the safest option.
Practical tips to stay compliant
To protect your deductions, it’s important to:
- Keep accurate odometer readings
- Retain your log book and supporting records for at least five years after lodging your tax return
- Review your log book regularly, especially if your work or business use of the vehicle has changed
If your log book is nearing the end of its five‑year life, or your usage has changed significantly, it’s often better to start a new 12‑week log sooner rather than later. That way, you reduce the risk of deductions being denied if the ATO reviews your claim.
Need help?
If you’re unsure whether your log book has expired, or you’ve recently replaced a vehicle and want to make sure it’s nominated correctly, please contact our office. We’re happy to help you work through the details and make sure everything is done properly.
Disclaimer: The information contained in this article is provided for general guidance only and does not constitute financial, taxation, legal, or other professional advice. While every effort has been made to ensure the accuracy and completeness of the information at the time of compilation, it may not address the specific circumstances, requirements, or objectives of you and/or your business.