This is the question that stops people two weeks in. They start a logbook, take a week off, and want to know whether they have to begin again.
The short version is in the answer above. The useful version needs the two requirements separated, because they are different things and people tend to merge them into one worry.
The two requirements are separate
The ATO’s wording is that the logbook must cover at least 12 continuous weeks, and that the period must be broadly representative of your travel throughout the year. Source: ATO, logbook method.
Continuity is about the period. It runs from a start date to an end date at least twelve weeks later, and it does not stop and resume. You do not get to log three good weeks in March, skip to a busy fortnight in June, and call it a period.
Representativeness is about the travel. The percentage the period produces has to be a fair reflection of how you use the car across the year.
Continuity is easy to satisfy and easy to break. Representativeness is the one that actually decides whether the number survives.
A quiet week does not break continuity
Twelve continuous weeks means twelve weeks in a row on the calendar. It does not mean you drove for work on every one of the days inside them.
If you were sick for four days, or the work dried up for a week, or you spent a week on a job you walked to, those days sit inside the period as days with little or no work travel. That is not a gap in the record. It is the record. Those low days pull your percentage down slightly, which is the correct outcome: they were part of the twelve weeks and they were part of how you used the car.
The instinct to pause the logbook through a quiet week and resume afterwards is exactly backwards. Pausing is what breaks continuity. Recording the quiet week honestly is what keeps the period intact.
Annual leave is the harder case
A week off is one thing. Three weeks away, with the car parked at the airport or not driven at all, is a different shape.
Nothing in the requirement says a period containing leave is invalid. But a twelve-week period of which three weeks were annual leave is, on its face, less representative of your working year than one without. The percentage it produces will understate your work use, and the question is whether it understates it enough to matter.
Two practical readings, neither of which is a rule:
- If the leave is short and your work travel resumed normally, the period is likely still broadly representative and the arithmetic runs against you rather than in your favour, which is the safer direction to be wrong in.
- If a large slice of the period was leave, you are better off starting the twelve weeks after you get back. Not because the earlier period is invalid, but because it is not representative and you will be claiming less than your actual use.
If leave is unavoidable inside the period and the percentage it produces looks clearly wrong to you, that is worth raising with a registered tax agent rather than resolving from a web page.
When to start so the period holds up
Choosing the start date is the single decision that most affects the outcome, and it is made before you have any data.
Start during ordinary work. Not during your busiest run of the year, and not during your quietest. The temptation is to begin the logbook the week the big job lands, because the percentage will look excellent. It will also be a percentage you cannot defend as representative, and it is the percentage you will then carry for five years.
Practical guidance:
- If your work is steady, any twelve weeks of normal trading will do. Start now rather than waiting for a better window.
- If your work is seasonal, pick a period that sits nearer the middle of the range than either end. A landscaper who logs only spring has not kept a representative logbook.
- Avoid starting immediately before known leave, a planned shutdown, or a stretch you already know is atypical in either direction.
- The period does not have to start on 1 July. It can start any day. The twelve weeks are counted from wherever you begin.
What actually breaks it
Four things, in rough order of how often they happen:
- Stopping and restarting. The period must run through. If you abandon it at week seven and pick it up in a month, you have two short periods and no logbook.
- Ending short. Eleven weeks and five days is not twelve weeks. If in doubt, run thirteen.
- Choosing a period you cannot defend as representative. Continuous and unrepresentative is still a failed logbook, and this is the failure that surfaces years later rather than immediately.
- Incomplete journeys inside the period. Missing purposes, missing destinations, or missing odometer readings undermine the entries themselves. Continuity does not rescue an entry that is not complete. See what a logbook has to contain.
After the twelve weeks
The logbook itself is finished. The percentage it produced can generally be used for that income year and the four following years, subject to conditions, which is what how long a logbook stays valid covers.
You still have an annual obligation after the period ends: odometer readings for each income year you use the method. That catches people who assume the logbook ending means the record-keeping ended. See what odometer readings you need.