Forgot Something on Your Tax Return? A Missing Slip or a Missed Claim

This page covers a return that left something out after you filed it: a slip you did not report or a claim you did not make. Each section below covers one kind of item. For the steps to change a filed return, see changing a return after you file.

A missing T4 slip

Leaving a T4 slip off your return is one of the most common filing errors. It happens most often when you had two jobs, left an employer mid-year, did seasonal or contract work, or misplaced a slip. (Employers file T4s; as an employee you report them.) The CRA already has a copy of every T4, so the question isn’t whether it will notice, but when, and the fix is straightforward. This page is part of the guide to filing a tax return in Canada.

Why the CRA already knows about your missing T4

Every employer must file T4 slips with the CRA by the last day of February after the tax year. The CRA’s systems match employer-reported T4 data against filed returns, and a return that’s missing T4 income gets flagged. This matching usually happens a few months after the filing deadline, so many people get a reassessment in late summer or fall.

What happens if the CRA finds it first

If you don’t correct the return yourself, the CRA issues a Notice of Reassessment that:

• Adds the missing income to your taxable income
• Recalculates your tax owing
• Charges arrears interest from the balance-due date (April 30) at the CRA prescribed rate, currently 7% a year, compounded daily
• May reduce a refund you already received or create a new balance owing

If the missing T4 made your refund too large, you’ll repay the difference plus interest. Correcting the return yourself before the CRA’s matching catches it is faster, and the guide to reading your Notice of Assessment explains the reassessment you’ll get either way.

If you haven’t filed yet

Include every T4 in the return: employment income goes on line 10100 and the income tax deducted on line 43700, for each slip.

If the filing deadline is close and a T4 still hasn’t arrived, you can file on time using your best estimate from your last pay stub, then correct the figures once the slip arrives. When you owe, filing late adds a late-filing penalty on top of interest, so an on-time return with a small error costs less than a late one.

How to fix a return you’ve already filed

Step 1: Find the missing T4

• CRA My Account. Under Tax information slips, select the tax year: every T4 your employers filed is listed, including ones you may have forgotten. The CRA My Account guide covers sign-in.
• The employer. Payroll can reissue a slip you’ve lost. If the employer has closed or can’t be reached, the CRA can help; its numbers are on the CRA contact information page.
• Your last pay stub. Box 14 (employment income) on the T4 matches the year-to-date earnings on your final stub of the year; how to read your pay stub explains the fields.

Step 2: Change the return

What to change for a missing T4:

• Line 10100: the corrected total employment income, including the missing slip
• Line 43700: the corrected total income tax deducted, adding Box 22 of the missing slip
• CPP and EI: add the slip’s CPP contributions (Box 16) and EI premiums (Box 18), so the return can credit them and work out any overpayment
• An explanation such as “Adding T4 from [employer name] not included in original filing”; a paper request includes a copy of the T4

You can submit the change online through My Account, through certified software, or on paper; the ways to change a filed return, and how long each takes, are on I made a mistake on my tax return.

Step 3: Pay any balance promptly

Once the CRA reassesses, paying the balance stops further interest. The ways to pay the CRA include My Account, online banking and Canada Post.

What you’ll likely owe

Adding a forgotten T4 almost always means more tax. The amount depends on:

• The employment income on the T4, taxed at your marginal rate
• CPP and EI: if your other employer didn’t reach the maximums, you may owe nothing extra; if both employers deducted independently, you may have over-contributed, and the excess CPP and EI is refunded when the return is reassessed
• Interest from the balance-due date on any additional tax

Two employers: why the second T4 often means a bill

Each employer withholds as if its job were your only income and applies the full basic personal amount (unless you told it otherwise on your TD1 form). With two jobs, too little tax is withheld overall, and adding the second T4 to the return brings the bill to the right level. This is one of the most common reasons for an unexpected balance; why do I owe taxes this year has a worked example and how to change withholding for next year.

What if your employer made the error?

If your employer left CPP contributions, EI premiums or income tax off the T4, or reported a wrong amount, ask the employer for an amended slip first. If it won’t correct it, the CRA can be contacted to resolve it. Employees are not penalized for an employer’s T4 errors once they are corrected.

More than one missing year

If you have several unfiled years or a pattern of unreported income that goes beyond a single slip, the Voluntary Disclosures Program lets you come forward and may waive penalties and some interest. Other slips left off a return have their own pages: unreported interest income, for example, covers a missing T5.

Medical expenses you forgot to claim

If you forgot to claim medical expenses on a prior year’s return, you can go back and recover the credit: CRA accepts changes up to 10 years back, so there is no time pressure. The parts specific to a missed claim are choosing the 12-month period, deciding whose return carries the claim, and correcting the right line. This page is part of our guide to filing a tax return.

Haven’t filed your current-year return yet? If it’s before the filing deadline and you haven’t submitted your return, there’s no need for an adjustment at all: just add the medical expenses in your tax software before you file. The tax deadline page shows how much time you have. Everything below applies once a return has already been filed.

The Credit in Brief

The medical expense credit is a non-refundable federal credit on eligible expenses above a threshold (the lesser of 3% of your net income or a fixed dollar amount that is indexed each year), plus a provincial credit at each province’s rate. The rates, the current threshold, worked examples and the full list of eligible expenses are on the medical expense tax credit page.

The 12-Month Period Trick

Medical expenses don’t have to be claimed January to December. You can claim any consecutive 12-month period ending in the tax year. This means if you had a large expense in November, you could claim from December of the previous year to November, potentially sweeping in more expenses from the prior year.

This can significantly increase your claim. Running the numbers for several 12-month windows shows which period produces the largest credit.

What Expenses Are Eligible?

Prescription drugs, dental and vision care, licensed practitioners’ fees, medical devices, private health plan premiums and medical travel are among the common eligible expenses; over-the-counter medications, vitamins, gym memberships and elective cosmetic surgery are not. The credit guide has the full table and CRA’s conditions for each.

Claiming for Multiple Family Members

You can claim eligible expenses for your entire household on one person’s return, so it is worth running the calculation both ways:

• Lower-income spouse: Their 3% threshold is smaller, so a greater portion of expenses exceeds it. This usually produces the larger credit.
• Higher-income spouse: If the lower-income spouse has no tax payable, the credit is wasted (it’s non-refundable). In that case, the higher-income spouse may generate more actual tax savings.

Donations can also be pooled on one spouse’s return; the guide to charitable donations you forgot to claim covers that fix and its own carry-forward rules.

How to Fix a Prior Year’s Return

Step 1: Gather receipts

Collect all eligible medical receipts for the year(s) in question. You don’t need to submit them with your adjustment, but CRA may request them in a review. Receipts are kept for at least six years.

Step 2: Identify the optimal 12-month period

Add up expenses by different 12-month windows to find the period where your total expenses most exceed the threshold.

Step 3: Correct line 33099 (or 33199)

Change line 33099 (you and your spouse’s medical expenses) to the corrected amount for the tax year, or line 33199 for other dependants (see below). Receipts don’t go with the request unless CRA asks for them. The three ways to submit the change, and their processing times, are covered in how to change a filed return.

What happens after you submit

CRA may accept the adjustment and issue a revised Notice of Assessment with any refund owing, request supporting receipts (originals are kept for six years), or deny it and explain why. A denial can be disputed if you disagree.

Medical Expenses for Other Dependants

For expenses paid for a parent, grandparent, older child, sibling, or other dependant who relies on you for support, claim on line 33199. The calculation is different: you subtract the dependant’s own net income from the eligible expenses, then apply the $2,834 or 3% threshold.

Charitable donations you forgot to claim

The charitable donation tax credit is one of Canada’s most valuable non-refundable tax credits, and one of the most frequently overlooked. If you forgot to claim past donations, you have two options: carry them forward up to 5 years, or go back up to 10 years and correct the original return. This page covers both, plus pooling a spouse’s receipts; it is part of our guide to filing your taxes.

The Credit in Brief

The federal credit has two tiers: a lower rate on the first $200 of donations in a year and a higher rate on the rest, with a further tier for donors in the top bracket. Each province adds its own credit on top. The current rates, a calculator and worked examples by province are on the charitable donation tax credit calculator page.

The 5-Year Carry-Forward Rule

If you didn’t claim donations in a prior year, you can carry them forward and claim them on any of the next 5 tax years. You are not required to claim donations in the year you make them.

Why you might deliberately carry forward:

• Your income was too low this year to benefit (non-refundable credit)
• You’re expecting higher income next year (moving into a higher tax bracket means the 33% tier applies to more of your donation)
• You want to pool multiple years of donations to maximize the amount above the $200 threshold

Expiry: Carry-forward donations expire after 5 years. Donations made in 2021 can be claimed on a return up to the 2026 tax year; after that, they cannot be claimed.

The 10-Year Look-Back (T1 Adjustment)

If you forgot to claim donations on a prior year’s return and that year is more than 5 years ago, you can still fix it by changing that year’s return, going back up to 10 tax years. A change requested in 2026 can go back to the 2016 tax year.

Claiming a Spouse’s Donations Together

CRA allows you to combine charitable donations from both spouses and claim them all on one return. This is almost always more advantageous, because:

1. More of the combined total exceeds the $200 threshold, qualifying for the higher 29% rate
2. The higher-income spouse’s return is usually more tax-efficient, since non-refundable credits reduce tax payable: you need tax payable to use them

Example: Both spouses donate $150. Claimed separately, each gets 14% on $150 = $21 each = $42 total. Claimed together on one return: 14% on $200 + 29% on $100 = $57, a $15 improvement.

If You Haven’t Filed Yet

If you simply haven’t filed this year’s return yet, there’s nothing to “fix”: just add the receipts before you submit. In your tax software, enter the donations on the charitable donations screen; it will automatically apply the 14%/29% federal credit on Line 34900 and calculate your provincial credit. Combining both spouses’ donations on one return (see above) usually gives a larger credit.

How to Fix a Prior Year’s Return

Step 1: Locate your official donation receipts

You must have official donation receipts from registered Canadian charities (CRA registration number format: 123456789 RR0001). Receipts from non-registered organizations do not qualify.

Check your email inbox, online charity portals, and prior tax files.

Step 2: Verify the charity is registered

Confirm the organization is a registered charity at canada.ca/en/revenue-agency/services/charities-giving/charities.

Step 3: Correct line 34900

Enter the donations on line 34900 of the return for the year you are claiming them in, using the amounts on the official receipts, and keep the receipts in case the CRA asks for them (a paper request includes copies). Online, software and paper options for sending the change are compared on I made a mistake on my tax return.

Step 4: Track your carry-forward balance

After adjustment, CRA will update your carry-forward donation balance on your Notice of Reassessment. Future tax software should automatically pull in the carry-forward amount.

Types of Eligible Donations

Not all giving qualifies for the donation tax credit:

Tip if you’re donating going forward: gifting publicly-listed securities (stocks, ETFs, mutual funds) directly to a registered charity, instead of selling them and donating the cash, eliminates the capital gains tax on that donation entirely, and you still get a receipt for the full market value. This doesn’t help a donation you’ve already missed, but it applies to future gifts.

Interest income you forgot to report

Interest income is one of the most commonly overlooked items on a Canadian tax return, particularly for people with multiple accounts, new HISAs, or compound GICs. The problem is that CRA gets T5 slip data directly from your bank, so any missing interest income is easy for them to catch. This page covers the interest-specific fix: which line, which slips, and how GIC accrual works. It is part of our guide to filing your tax return.

Why CRA Already Has This Information

Every bank, credit union, and financial institution that pays you $50 or more in interest per year must issue a T5 slip (Statement of Investment Income) and file a copy with CRA by the end of February. CRA’s systems cross-reference this data against your filed return.

If you earned less than $50 in interest from a given institution, they may not issue a T5, but you are still required to report that income. Many Canadians miss small interest amounts because they never received a slip.

What Counts as Interest Income (Line 12100)?

Interest isn’t the only investment income CRA cross-matches. Dividends and capital gains go on different lines, and mixing them up is another common mistake. If a whole T4 is missing too, see what to do when you forgot a T4 slip.

The T5 slip covers interest and dividends; the T3 slip covers income from trusts, mutual funds, and ETFs, and T5008 slips report proceeds from investment dispositions (capital gains).

GICs and Accrued Interest

For compound (non-cashable) GICs with a term longer than one year, CRA requires you to report accrued interest on each anniversary date, even before you receive the cash. This catches many people off guard when a 5-year GIC matures.

For example, if you hold a $50,000 compound GIC at 4%, you must report approximately $2,000 in interest income each year of the GIC’s term, not all $10,800+ when it matures.

What Happens If CRA Finds It Before You Fix It

CRA will issue a Notice of Reassessment that:

1. Adds the missing interest income to line 12100
2. Recalculates your tax owing at your marginal rate for that year
3. Adds arrears interest from April 30 of the filing year at CRA’s prescribed rate (currently 7% annually, compounded daily)
4. Adjusts any income-tested benefits (the Canada Child Benefit, GIS, GST credit) that were calculated based on the understated income

Honest errors that you proactively correct are generally treated as errors, not evasion: you’ll owe the arrears interest above but no penalty. The civil gross-negligence penalty (50% of the understated tax) generally applies only when there’s a pattern of wilful omission or the amounts are very large, and it’s far more likely to be assessed if CRA catches the omission first rather than you disclosing it via a T1 Adjustment.

How to Fix It

Step 1: Find all missing T5 slips

Log in to CRA My Account → Tax information → Tax slips. CRA posts T5 data from all institutions that filed slips in your name. You can also check your online banking portals: most financial institutions provide tax documents under “Documents” or “Tax Centre.”

Step 2: Correct line 12100

For each year with missing interest, line 12100 needs the corrected total: slip interest, interest with no slip, and accrued GIC interest. Attach the T5s to a paper request. Whichever way you send the change (My Account, software or Form T1-ADJ, all explained on the guide to fixing a filed return), the CRA accepts adjustments up to 10 tax years back.

Step 3: Pay any balance

Arrears interest keeps compounding daily on the extra tax until the balance on the reassessment is paid. Payment options:

• CRA My Account, Make a payment
• Online banking, with the CRA added as a payee
• Canada Post outlet with a remittance voucher

Multiple Years of Unreported Interest

If you have several years of unreported interest income, the Voluntary Disclosures Program lets you come forward proactively and may result in partial interest relief and waiver of gross negligence penalties. A tax accountant can help assess whether it fits your situation.

How to Avoid Missing Interest Income in Future Years

• Download your T5s early: most banks post them in online banking by mid-February
• Check CRA My Account: all T5s filed on your behalf appear there by April
• Track GIC anniversaries: note when compound GICs accrue reportable interest
• Consolidate accounts: fewer institutions means fewer slips to track
• Watch joint accounts: each account holder must report their proportional share, and it’s easy to assume the other person is claiming it
• Include foreign accounts: interest from a foreign bank or investment account is still taxable in Canada even when no Canadian slip is issued

Related pages

• Changing a return after you file
• Medical expenses tax credit
• Charitable donations tax credit
• The T4 slip
• The T5 slip
• How to file a tax return in Canada
• Tax deductions and credits: the full list