The simplified logbook

You do not have to log every trip every year. After one full base year, a sample period can stand in for the year, as long as it stays close to the base year.

Step 1: a full base year

Keep a complete logbook for 12 months. Revenu Québec states that the base year does not have to be a calendar year.

Step 2: a sample period in a later year

Keep a logbook for a sample period of at least three consecutive months. Then:

Calculated business use = (sample % ÷ base-year % for the same months) × base-year annual %

Step 3: the two checks

• The sample period must be within 10 percentage points of the base year's same months.
• The calculated annual use must be within 10 percentage points of the base year's annual use.

If either check fails, the base year no longer represents your normal use. Keep a new full-year logbook to set a new base year. The CRA text says "within 10%", but its own example applies the test in percentage points. Revenu Québec says "10 percentage points" explicitly.

The official examples

• CRA: base year 49%, same months 46%, sample 51%. (51 ÷ 46) × 49 = 54%, within the 39% to 59% band.
• Revenu Québec: base year 60%, same months 57%, sample 65%. (65 ÷ 57) × 60 = 68%.

Check your own numbers