What is the 90-day logbook?
The short answer
IRD lets you set your business-use % from a logbook kept for at least 90 days, and use it for up to three years. WorthMile sets yours once your shifts with odometer readings cover at least 90 calendar days and pass the checks below.
What has to be true
- At least 10 shifts with start and end odometer readings in those 90 days or more. They don’t have to be 90 working days.
- No gap of more than 21 days between shifts.
- The same car throughout, and odometer readings that never go backwards.
Fewer than 10 shifts doesn’t start the period again: it stays open from the same start date and is set when your 10th shift arrives. A long gap or an odometer that goes backwards does start it again, after the break. This version tracks one car; changing cars isn’t supported yet. Either way a logbook can stay unset after 90 days. Until it’s set, your business-use % is a live estimate.
If your driving changes a lot, by more than a fifth either way, the Tax page suggests a new logbook. Tap Start a new logbook to begin another 90 days.
The Logbook evidence PDF, under For your accountant, is available once your logbook is set.