Bookkeeping mistakes rarely announce themselves. Nobody gets a letter saying a business overpaid tax by $4,000 because sales tax on business purchases was never claimed properly. The money simply never arrives, year after year, and the owner has no reason to suspect anything is wrong.
That is what makes these errors expensive. They are not dramatic. They are structural, they repeat every month, and they compound. Here are the seven that cost Canadian small businesses the most — and what fixing each one is actually worth.
1. Not claiming every input tax credit you are entitled to
If you are registered for GST/HST, you can claim back the tax you paid on business purchases. Most owners know this. Far fewer capture all of it.
The leakage happens in predictable places: software subscriptions charged to a personal card, mileage and vehicle expenses, home-office costs, professional memberships, cell phone bills, and anything bought while travelling. Each individual amount is small enough to feel not worth chasing. Across a year they are not small.
A business with $60,000 of legitimate taxable expenses that captures only 70% of its input tax credits is leaving roughly $900 with the government annually. Over five years that is a real number, and it is a number you were entitled to keep.
The fix: one dedicated business card, every business purchase on it, no exceptions. Reconstructing this from memory in March never works.
2. Registering for sales tax at the wrong time
The federal small-supplier threshold is $30,000 in taxable revenue. Cross it and GST/HST registration becomes mandatory. Miss the crossing and you owe the tax on sales you never collected it on — out of your own margin.
In British Columbia there is a second, lower trigger that catches people out: the PST registration threshold sits at $10,000, well below the federal figure. A BC business can comfortably be below the GST threshold and already required to register for PST.
There is also a case for registering voluntarily before you have to. If you sell mainly to other registered businesses, the GST you charge costs your customers nothing — they claim it back — while you immediately start recovering the tax on your own purchases. For a business with significant startup costs that is often worth doing on day one.
3. Missing payroll remittance deadlines
This is the most expensive item on the list, and it is entirely mechanical.
CRA penalties on late remittances scale with how late you are: 3% at one to three days, 5% at four to five, 7% at six to seven, and 10% once you pass seven days late. There is no proportionality below those thresholds — being one day late and being three days late cost exactly the same.
Look at the shape of that schedule. The jump from 7% to 10% happens at the one-week mark, which means a business under cash-flow pressure faces its steepest penalty increase at precisely the moment it is most tempted to wait for a customer payment to land. On a $25,000 remittance, crossing that line costs $750.
The fix is a calendar reminder three days before every due date, and treating remittance funds as money you are holding rather than money you have.
4. Running personal and business money through the same account
Every bookkeeper has met the client who says they will sort it out later. Later costs more than they think.
Mixed accounts create three separate problems. Bookkeeping fees rise, because someone bills by the hour to determine whether a transaction was groceries or a client lunch. Legitimate deductions get missed, because in a list of four hundred mixed transactions the business ones become invisible. And if the CRA ever reviews the file, a commingled account weakens your position on every judgement call in it.
Separate accounts cost almost nothing and take twenty minutes to open. This is the cheapest fix on this list by a wide margin.
5. Reconciling once a year
Bookkeeping done annually is not bookkeeping. It is archaeology.
A duplicate charge caught in February is a five-minute correction with the vendor. The same duplicate found the following March is unrecoverable — the vendor’s dispute window closed months ago. A customer who was never invoiced is collectable in week three and is usually written off after fourteen months.
The larger cost is decision-making. An owner working from year-old figures is making pricing, hiring and purchasing decisions on numbers that no longer describe the business. Monthly reconciliation is not primarily a compliance exercise; it is the only way the financial statements say anything useful while you can still act on them.
6. Ignoring the provincial layer
Federal rules are uniform. Provincial obligations are not, and they are where multi-province businesses get caught.
In British Columbia, the Employer Health Tax applies once B.C. remuneration exceeds $1,000,000 — 5.85% on the portion between $1,000,000.01 and $1,500,000, then 1.95% of total remuneration above $1,500,000. A growing BC business can cross that threshold mid-year without anyone noticing until the return is due.
Alberta has no equivalent payroll levy and no provincial sales tax, which is genuinely simpler. But a business operating in both provinces does not get to average the two systems. It has to run both correctly, and the BC side carries obligations the Alberta side does not.
7. Doing it yourself long after it stopped making sense
There is a stage where owner-managed bookkeeping is the right answer. A sole trader with thirty transactions a month and one bank account should absolutely keep doing their own books.
The problem is that almost nobody revisits the decision. The business grows, transaction volume triples, payroll starts, sales tax registration arrives, and the bookkeeping approach stays exactly as it was — except now it takes an evening a week and the owner is the constraint on their own growth.
The honest test is not whether you can do it. It is what those hours would produce elsewhere. An owner spending six hours a month on bookkeeping is spending seventy-two hours a year — nearly two working weeks — on a task that a professional completes in a fraction of the time and that a firm handling small business bookkeeping in Burnaby, BC or your own local market would price at a small fraction of what those hours are worth in revenue-generating activity.
There is a second benefit that owners consistently underrate: someone who sees a hundred sets of books notices patterns in yours that you cannot see, because you have no comparison. Margin drift, a supplier whose prices crept up, a customer segment that costs more to serve than it pays. That perspective is not something better software provides.
What to do this month
You do not need to fix all seven at once. Fix them in order of cost.
• Set remittance reminders today. This is the largest single downside on the list and takes five minutes to eliminate.
• Separate your accounts this week if they are still mixed.
• Check your sales tax registration status against both the $30,000 federal and, in BC, the $10,000 provincial threshold.
• Commit to monthly reconciliation — one recurring appointment, same day each month.
• Then calculate what your bookkeeping hours are actually costing you, and decide deliberately whether to keep them.
None of these are sophisticated financial strategies. They are maintenance. But maintenance is where most of the recoverable money in a small business actually sits — quietly, in the same places, every single year.
Sources
— Canada Revenue Agency — GST/HST small supplier threshold and input tax credits
— Canada Revenue Agency — penalties for failing to remit source deductions
— Province of British Columbia — Employer Health Tax and PST registration requirements
About the author
Contributed by BMTS Corp, a Canadian accounting and bookkeeping firm serving small businesses in British Columbia and Alberta. All tax figures reflect rules current for 2026.
