Starting a Mileage Log Mid-Year: What It Covers

Most people who keep a vehicle logbook did not start it on January 1. They started it the week they read that the CRA expects one, which for a lot of self-employed people is somewhere around August, when a bookkeeper asks or a friend gets a review letter.

The question that follows is always the same: is a log that starts in August worth anything for the year, or is the year already lost? The answer is that it is worth a great deal, but not in the way people hope. A partial log is strong evidence for the months it covers. It is not a sample that can be stretched over the rest of the year, and the CRA's rule that lets you keep a short log in later years does not reach the year you start in.

This page separates the three things a mid-year start touches: the months already gone, the months you log from now on, and the year after, which is where starting today pays off most.

What the CRA expects for a full year

The CRA's motor vehicle records page calls an accurate logbook of business travel maintained for the entire year the best evidence of business use. For each business trip it asks for the date, the destination, the purpose and the kilometres, and it asks for the odometer reading of each vehicle at the start and end of the fiscal period. The full field-by-field list is in the logbook requirements guide.

That matters because of what the log is for. A sole proprietor or partner claims actual vehicle costs (fuel, insurance, repairs, interest, capital cost allowance) multiplied by the business-use percentage on the T2125, and the percentage is business kilometres divided by total kilometres for the fiscal period. Both halves of that fraction cover the whole period. A log that starts in August supplies part of the top and part of the bottom, and nothing about January to July. How the fraction itself is built is covered in calculating your business-use percentage.

What a partial log supports

For the months it covers, a log kept as you drive is exactly the evidence the CRA ranks first. August to December, logged trip by trip with the four fields, is five months of best evidence. Nothing about starting late weakens those entries.

What it does not do is speak for the months before it. The CRA's own wording on a related situation is the closest guide. When a sample logbook fails its test, the CRA says the logbook "would only be reliable for the three-month period it had been maintained", and that for the remainder of the year business use "would need to be determined based on an actual record of travel or alternative records". A log is evidence of the period it was kept in. The period it was not kept in needs its own support.

Why the August percentage cannot be stretched over the year

The tempting move is to take the percentage from the months you logged and apply it to the whole year. If August to December came out at 50%, claim 50%.

The CRA does have a method for projecting a short log over a full year. It is the simplified logbook, and it is explicit about its precondition: "After one complete year of keeping a logbook to establish the base year, you can use a three-month sample logbook." The projection compares the sample against the same months of a full base year, and then tests the result against the base year's annual figure. How that formula works, with the CRA's own example, is in the simplified logbook guide.

In the year you start, there is no base year. There is nothing for the months you logged to be compared against, so there is no CRA method that turns five logged months into a twelve-month percentage. Applying the August percentage to January is not a projection the CRA recognises. It is an assumption that the first seven months looked like the last five, and a log kept from August cannot prove that, because it did not exist yet.

Seasonal work makes the gap concrete. A landscaper who starts logging in August has missed the spring rush. A tutor who starts in August logs a quiet month and then the school year. Either way, the late months say little about the early ones.

Covering the months before you started

The months before the log need what the CRA calls an actual record of travel or alternative records. In practice that means rebuilding the business trips from documents made at the time: invoices and quotes with a job address, calendar entries, emails arranging visits, supplier receipts, phone location history. Each trip gets its date, destination and purpose from a document, and its distance from a mapped route rather than from memory.

That is a job with its own method and its own limits, and it is set out step by step in rebuilding a mileage log the CRA can accept, including what the Tax Court has done with reconstructions that worked and ones that did not. Two points from it matter most for a mid-year start:

• Label it as a reconstruction. The early months are rebuilt, dated the day you rebuilt them, and say what they were built from. They sit beside the real log, not inside it.
• Count only what you can evidence. A reconstruction will usually find fewer business kilometres than a guess would. The honest figure for January to July may well be lower than the August to December figure, and that is fine.

The earlier months also need an odometer reading at the start of the fiscal period. If you did not photograph it on January 1, service, inspection and repair invoices on either side of that date are the usual way back to it, and the reconstruction guide shows the arithmetic.

A worked example: an established business that starts logging on August 1

A self-employed renovator, carrying on business for several years, December 31 year end, one vehicle. She starts a full log on August 1, 2026 and photographs the odometer that morning. Her January 1, 2026 reading is recovered from service invoices using the method in the reconstruction guide. The inputs:

Reading	Date	Odometer
Start of fiscal period (recovered from service records)	2026-01-01	52,400
Log starts (photographed)	2026-08-01	63,900
End of fiscal period (photographed)	2026-12-31	71,300

That splits the year's driving into two blocks.

Block	Total km	Business km	Source of the business km	Business use
January 1 to July 31	11,500	4,600	Rebuilt from invoices, calendar and supplier receipts, mapped distances	40.0%
August 1 to December 31	7,400	3,700	Kept as she drove	50.0%
Fiscal period 2026	18,900	8,300		43.9%

The totals: 71,300 minus 52,400 is 18,900 km for the year, and 11,500 plus 7,400 checks back to it. Business kilometres are 4,600 plus 3,700, which is 8,300. Business use is 8,300 divided by 18,900, which is 43.9%.

Now the tempting version. Applying the August to December figure of 50.0% to the full 18,900 km would claim 9,450 business kilometres. That is 1,150 km more than the records support, every one of them in months the log did not cover. On her actual vehicle costs, each percentage point is one hundredth of the year's fuel, insurance, repairs, interest and capital cost allowance, and the gap here is 6.1 points that nothing in her file backs.

Notice also what the example does not do. It does not treat the two blocks as equally strong. The August to December block is a contemporaneous log. The January to July block is a reconstruction, and it should be kept with its cover note and its source documents, so that anyone reviewing it can see which is which.

Why starting today still matters, even late in the year

There are two reasons, and the second is the bigger one.

First, every month you log is a month you do not have to rebuild. The reconstruction for January to July is work, and it is weaker evidence than a log. Starting in August instead of waiting until January cuts five months out of next spring's rebuilding and replaces them with the best evidence the CRA recognises.

Second, the log you start now is the beginning of a base year. The simplified logbook needs one complete year of full logging before a three-month sample is available in later years. The CRA describes the base year as "one complete year" of keeping a logbook, and when it tells people to start again it speaks of maintaining a logbook for "a new 12-month period". What it asks for is one complete twelve-month period of full logging, and the log you start today is the first month of it.

The simple way to have a base year nobody can argue with is not to stop at twelve months. The renovator above started on August 1, 2026. If she keeps the full log through December 31, 2027, she has more than a complete twelve-month period, and she has her whole 2027 fiscal year logged in full, so the base year's annual percentage and its quarterly percentages line up with a year she actually claimed. From 2028 she can keep a three-month sample instead of a full log, as long as her driving in the base year remains representative of her normal use and the calculated figure stays within ten points of the base year's annual figure.

One more thing about that base-year log: it is kept longer than ordinary records. The CRA requires the full twelve-month logbook to be kept six years from the end of the tax year for which it was last used to establish business use, not six years from the year it was kept.

A new business that starts mid-year

Everything above is about an established business with a year already running. A business that starts partway through the year is a different case, and a better one.

Self-employed individuals generally have to use a December 31 year end. The Income Tax Act says an individual's fiscal period cannot end after the end of the calendar year in which it began, unless the individual uses the alternative method in subsection 249.1(4), and the CRA's guide says a fiscal period can be shorter than twelve months "such as when a new business starts". So a business that begins on August 15, 2026 has a first fiscal period of August 15 to December 31, 2026.

That changes what "partway through the year" means:

• A log that starts on the first day of the business is a full log. It covers the entire fiscal period, which is the period the CRA asks about. There are no earlier months to rebuild, because the business did not exist in them.
• The odometer readings bracket the business, not the calendar. The CRA asks for the reading at the start and end of the fiscal period, so the first photo is on the day the business starts. Kilometres driven before that are not in the fraction at all. If you buy or replace the vehicle during the period, the CRA also asks you to record the date and the odometer reading when you buy, sell or trade it. The readings themselves are covered in odometer readings at the start and end of the year.
• Capital cost allowance is prorated. Under section 1100(3) of the Income Tax Regulations, when a taxation year is less than twelve months, the maximum CCA is reduced to the number of days in the year over 365, and section 1104(1) makes that "year" the business's fiscal period when it does not match the calendar year. A short first period means a smaller CCA claim on the vehicle. The class rules are in the CCA guide.
• The first period is not a base year. It is shorter than twelve months, so it cannot be the complete year the simplified logbook needs. Keep the full log going through the next complete fiscal period, the same way the renovator above does.

The same reasoning applies if you were an employee until the summer and went self-employed after. The business's fiscal period starts when the business starts, and the kilometres you drove before then are not part of the T2125 fraction.

Getting a late start right

• Photograph the odometer the day you start, with the date visible or noted. It anchors the logged block.
• Log every business trip from that day, with all four fields. Date, destination, purpose, kilometres. A trip with no purpose is half a record.
• Keep the logged months and the rebuilt months apart. Two files, or one file with a clear line and a cover note. Never merge the reconstruction into the log as if it had been kept at the time.
• Get the January 1 reading, or the business's first-day reading, from service records if you did not take it.
• Photograph the odometer on the last day of the fiscal period.
• Keep going through the next full fiscal period if you want the simplified logbook available afterward.

If the habit is what stops you, Claimable Drive, in beta for iPhone, records drives in the background, you swipe each one business or personal, and it works out the business-use percentage from those swipes.

FAQ

Can I start a mileage log in the middle of the year? Yes, and you should start the day you realise you need one. The log is strong evidence for the months it covers. The months before it need their own support from records made at the time, and the year's percentage is built from both blocks, not from the logged months alone.

Can I use the percentage from my partial log for the whole year? Not on the strength of the log alone. The CRA's method for projecting a short log over a full year is the simplified logbook, and it is only available after one complete year of full logging establishes a base year. In the year you start, there is no base year to project from.

Is a partial-year log a three-month sample logbook? No. A sample logbook is a later-year tool that is measured against a full base year. A log kept for part of your first year is simply a full log of the months it covers.

When can my base year start? The CRA describes it as one complete year, or a 12-month period, of full logging. The cleanest approach is to keep the full log running through the end of your next complete fiscal year, so the base year's figures line up with a year you claimed.

I started my business in August. Do I need a log for January to July? No. Your first fiscal period starts when the business starts and, for most individuals, ends on December 31. A log that begins on your first business day covers the whole fiscal period. Photograph the odometer on that first day as your starting reading.

Does my first short fiscal period count as a base year? No. It is less than twelve months, so it is not one complete year. Keep the full log through your next complete fiscal period.

Sources

1. CRA, Motor vehicle records, the full logbook as the best evidence, the four trip fields, the odometer at the start and end of the fiscal period and on a change of vehicle, the simplified logbook and its base year, the "actual record of travel or alternative records" wording, and the retention rule for the base-year logbook.
2. CRA Guide T4002, Chapter 1, How to report your self-employment income, the fiscal period, shorter periods when a new business starts, and the December 31 year end.
3. CRA Guide T4002, Chapter 3, Line 9281, Motor vehicle expenses, the logbook fields and the simplified logbook for the self-employed.
4. Income Tax Act, section 249.1, the definition of fiscal period, subsection (1)(b) for individuals and subsection (4) for the alternative method.
5. Income Tax Regulations, section 1100, subsection (3), capital cost allowance for a taxation year of less than twelve months.
6. Income Tax Regulations, section 1104, subsection (1), taxation year read as the fiscal period of a business that does not coincide with the calendar year.