Mileage guide
CRA three-month logbook: check the base year before using a sample
By FlatMile ·
General Canadian self-employed recordkeeping information. The CRA simplified logbook has eligibility conditions.
At a glance
The CRA's simplified logbook is a later-year sampling method built on a complete base-year log. Three months alone do not establish a first-year annual business-use percentage. Keep the full-year evidence and test whether the later year remains representative before relying on a sample.
The CRA guidance compares the sample with the same period in the base year, then applies that ratio to the base year's annual business use. Its example interprets the permitted annual range as ten percentage points above or below the base-year figure. The sample must still represent normal use; contradictory evidence matters.
Collect the inputs before doing arithmetic
Put these items together in one worksheet:
- Identity of the vehicle and the full base-year reporting dates.
- Base-year total and business kilometres for the whole year.
- Those same figures for the matching three-month period.
- Later-year total and business kilometres for the sample period.
- Notes about changes in work, routes, personal use or vehicle availability.
If the old log only contains one annual percentage, retrieve its dated trips before attempting the comparison. A January–March sample cannot be compared with an arbitrary summer quarter just because the totals are easier to find.
Follow an original worked example
This fictional example deliberately uses round values to make each step checkable. It is separate from the example on the CRA website.
| Input | Total kilometres | Business kilometres | Business share |
|---|---|---|---|
| Complete base year | 20,000 | 8,000 | 40% |
| April–June in the base year | 5,000 | 2,500 | 50% |
| April–June in the later year | 5,000 | 2,750 | 55% |
The calculation is 55% ÷ 50% × 40% = 44%. Compared with the base-year 40%, that is four percentage points higher. It falls inside the numerical 30%–50% range for this illustration, but the numbers alone do not prove the sample represents the rest of the year.
Now suppose the later sample's business share were 70%. The same calculation would produce 56%, outside that range. The CRA says an unsuitable sample cannot establish the whole later year: the remainder requires actual travel records or other supporting records. Consider a new full base year when the pattern changes.
Write down what changed
Before accepting the worksheet, compare your business diary with the previous year's. A new delivery contract, a move closer to customers or a long personal road trip can explain why a convenient quarter gives a misleading picture.
Use a short exception note: what changed, when, which vehicle was involved and which records support it. Do not edit a sample's dates after seeing the answer simply to obtain a preferred percentage. Preserve the dates you used and the reasoning for their relevance.
If you cannot explain the difference, continue recording journeys while you resolve it. Keeping additional evidence is more useful than discovering at filing time that the unrecorded months cannot be reconstructed.
Preserve the base year as an active record
Store the base-year file beside each later worksheet that relies on it. The CRA states that the full base-year log must be retained for six years after the end of the last tax year that uses it. A base year reused over time therefore remains relevant beyond its original filing date.
Save a readable copy of the log, the calculation and the underlying distance totals. A screenshot of the final percentage omits the evidence needed to reproduce it. If multiple vehicles are involved, use the full vehicle-record workflow to keep their records separate.
This guide is a worksheet for checking the method with your preparer. It does not promise acceptance of a particular sample or replace records for individual expense rules.