Updated Checked by the Tax-Services.ca editorial team How we check
Duplicate transactions in your books usually come from one source: a bank feed and a manual entry both recording the same payment. Left alone, a single doubled $1,130 supplier bill in Ontario overstates your expenses by $1,000 and your HST claim by $130. Finding them is a matching job, and once you know where to look it isn’t slow.
Where do duplicate transactions come from?
Four places, mostly. A bank feed imports a payment and someone types the same one in. A receipt gets scanned twice, once from the email and once from the phone. A recurring entry runs on top of a manual one. And a card payment shows up as an expense and again as a transfer.
The bank never makes the mistake. Your books do. So the statement is your referee.
How do you spot one?
Sort the list by amount, then by date. Two lines with the same amount and same supplier within a few days deserve a look. Real repeats exist (two coffees on one card, a monthly fee), so check the reference or invoice number before you delete anything.
Your accounting software may flag likely matches, so turn that on. It won’t catch everything. A payment of $1,130 entered as $1,113 in one place and $1,130 in another slips straight past a same-amount test. Only a bank reconciliation catches that, because the ending balance won’t match.
Here’s a quick routine for a clean-up day. Reconcile the bank account for one month. Whatever doesn’t tick off against the statement is a suspect. Do the same for the card, then for any account that feeds your books automatically. Three accounts, a couple of hours, and most owners find at least one pair they’d missed.
What do duplicates do to your tax numbers?
They inflate whatever they touch. We ran a $1,000 purchase through the GST/HST calculator for three provinces to show the sales tax inside a single bill.
| Province | Bill before tax | Tax | Bill total |
|---|---|---|---|
| Ontario (13% HST) | $1,000.00 | $130.00 | $1,130.00 |
| Alberta (5% GST) | $1,000.00 | $50.00 | $1,050.00 |
| British Columbia (5% GST, 7% PST) | $1,000.00 | $120.00 | $1,120.00 |
Your own situation decides how much of that tax you can claim back as an input tax credit, and we haven’t tested the BC PST rules here. The pattern is what matters: a duplicate bill doubles both the expense and the credit you claim, and it does so quietly, because nothing on the screen looks wrong until the bank statement disagrees.
The same works on sales. Record a $2,260 Ontario invoice twice and you report $2,000 of extra revenue and $260 of HST you never collected. Your return then says you owe more than you do. That’s the milder error. Doubled expenses and credits are the ones that draw attention, because you’ve claimed money you weren’t entitled to.
If you’re unsure which part of a total is tax, the HST reverse calculator pulls it out of a receipt.
What should you do once you find one?
Delete or void the extra entry and leave a note, not a blank. Then check whether the mistake reached a filed return. If it did, you’ll need to correct that return. We haven’t confirmed the CRA’s current process for GST/HST corrections, so look at canada.ca or ask your accountant before you file an amended return.
Don’t delete the bank line. It’s real money, even if it’s only a few bucks.
Also check that nothing was paid twice. If a supplier really was paid twice, ask for a credit or refund and record that as its own transaction. A doubled payment is common with e-transfers sent from a phone on a slow connection. The same goes for payroll. A doubled entry can throw off your remittance, and the payroll remittance calculator gives you a benchmark for what a period should look like.
Is it a duplicate, or two real payments?
Ask three questions. Do the dates match the bank, line for line? Is there a distinct invoice or reference number on each? Did the supplier actually deliver twice? If the answer to all three is no, it’s a double. If the invoice numbers differ, leave both alone and move on. A monthly subscription charged twice in one month on different days is a bank problem, not a bookkeeping one, so call the vendor.
How do you stop them coming back?
Pick one route in for each source. If the bank feed brings in card payments, don’t type them. Name files by supplier, date and invoice number so a second copy clashes. Reconcile every month, not once a year. And limit who can add entries, since three people posting to one ledger is where most doubles start.
One habit helps. Before you post an invoice, search for the supplier and the amount.
Limits: our figures use single purchases at 2026 rates, without discounts, rebates or partial-credit rules. The profit margin calculator shows how expenses feed into your margin if you want to see the effect on profit. Also remember that the CRA says you’re responsible for your records even when a bookkeeper keeps them, and that they must be kept for six years.
Our sources
Tax rates in the table come from our GST/HST calculator, which uses 2026 federal and provincial rates. The record-keeping rule comes from the Canada Revenue Agency’s page on keeping records, read on 30 September 2026. We’re an independent site, and no government body is behind it.
Frequently asked questions
Why do duplicate transactions happen so often?
Usually two routes bring in the same payment, such as a bank feed plus a manual entry, or a receipt scanned twice.
Should I delete the bank line or my entry?
Delete or void your extra entry. The bank line reflects real money and stays.
Do duplicates change my GST/HST return?
Yes if they touch sales or purchases. A doubled bill doubles both the expense and the tax credit you claim.
What if the duplicate is already on a filed return?
You will likely need to correct the return. We did not confirm the CRA's current process, so check canada.ca or ask your accountant.
Does my accounting software find them all?
No. It usually flags matching amounts and dates, but misses entries where an amount was typed differently. A monthly bank reconciliation catches those.
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