Your first Canadian tax return isn't a test you can fail, but it is easy to hand over money you didn't need to. Every spring, the same handful of first-time errors lands on the same desks: a T4 that never made it into the software, a credit nobody mentioned, an RRSP contribution claimed in the wrong year.
The encouraging part is that almost all of these can be fixed, usually without a penalty, and the habits that prevent them take about twenty minutes to learn.
Assuming you don't need to file
If you earned only a few thousand dollars this year, or spent most of it in a classroom, it's tempting to skip the return entirely. That's often a mistake. Filing is what triggers several refundable payments you can't get any other way: the GST/HST credit, the Canada Workers Benefit for eligible low-income earners, and provincial programs such as Ontario's Trillium Benefit. No return, no payments.
Filing also starts your record with the Canada Revenue Agency: it builds RRSP contribution room and gives you proof of income for a mortgage, a rental application or a student loan. Doing it with no balance owing costs nothing but time.
Missing slips and income that never arrives on a slip
Employers, banks, universities and pension administrators all send copies of your slips to the CRA, so a missing T4 rarely stays missing for long. Before you file, register for CRA My Account and use the Auto-fill my return feature in certified tax software. It pulls the slips the agency already has on file, which is the fastest way to spot one you forgot.
The trickier problem is income nobody reports for you. This includes:
- Tips and cash paid for casual work
- Ride-share, delivery and freelance income, even when no T4A was issued
- Proceeds from selling cryptocurrency, stocks or a rental property
- Foreign income, including some accounts and investments held outside Canada
If a slip arrives after you've filed, you adjust the return. You don't start over.
Leaving credits and deductions unclaimed
First-timers tend to claim the one or two credits their software prompts them for and stop there. Non-refundable credits reduce tax owing, and unused amounts can sometimes be carried forward or transferred to a spouse or parent. Worth a careful look:
- Tuition amounts from a T2202, plus unused tuition carried forward from earlier years
- Interest paid on government student loans
- Medical expenses, which you can claim for any 12-month period ending in the tax year, so pick the stretch that captures the biggest bills
- Charitable donations, which can be combined with a spouse's for a better rate
- Moving expenses, if you moved at least 40 kilometres closer to school or work
- Child care costs, the disability tax credit, and the caregiver credit where they apply
- Provincial rent and property tax credits, which plenty of people never know exist
Keep the receipts. Most claims aren't submitted with the return, but the CRA can ask to see them later.
The RRSP deadline mix-up
Contributions made in the first 60 days of a year can be deducted against either the previous year's income or a future one. That choice is yours, and it's made on the return, not at the bank. A contribution made in February 2026 can go on your 2025 return, but it doesn't have to.
Two related traps: claiming a deduction for money you never actually contributed, and putting in more than your room allows. There's a $2,000 lifetime buffer before penalties apply, but it isn't a free top-up. Check your Notice of Assessment or CRA My Account for your exact limit before you deposit anything.
Confusing the filing deadline with the payment deadline
April 30 is the date most people know. Self-employed filers and their spouses get until June 15 to file, but any balance owing is still due April 30, with interest running from that day. Filing on time with no money to pay is far better than ignoring the whole thing: the late-filing penalty is a percentage of what you owe, and it grows every month it sits there.
Missing the deadline can also interrupt benefit payments tied to your return, which is a slow and irritating way to lose a GST credit you were counting on.
Fixing a return you've already sent
Errors are correctable, and the CRA expects some. If you filed through NETFILE and the same season is still open, use ReFILE. Later, use Change My Return in CRA My Account, or mail a T1 adjustment request. You generally have up to ten years to ask for a change.
If the mistake means you owe more, pay the difference as soon as you spot it to stop the interest. If it means you're owed more, adjust right away rather than waiting for the CRA to notice.
A short routine for next spring
None of this is complicated once it becomes a habit:
- Collect every slip in one folder as it arrives, starting in January.
- Check CRA My Account and let Auto-fill pull what the agency already has.
- Walk through the credits list before you submit, not after.
- Decide which year your RRSP contributions belong to, and mark the 60-day deadline.
- File well before April 30, and pay anything you owe by that date no matter when you file.
- Keep your Notice of Assessment
Photo: stevepb / Pixabay
