Updated Checked by the Tax-Services.ca editorial team How we check
To calculate your tax return, take the tax you owe for the year and subtract what was already withheld from your pay. Say you earned $75,000 in Ontario and $14,000 came off your cheques: the estimate is a refund of $1,295.35. Deductions raise that refund and extra income lowers it, and the steps below show how.
How do you calculate your tax return step by step?
The path is the same every year. Add up income from every slip, subtract deductions to get taxable income, work out federal and provincial tax, then take off your credits. What’s left is your tax for the year, and you set it against what payroll deductions or instalments already covered.
Think of it as a bank statement for the year. Money in is your income, money out is the tax, and what your employer already sent the taxman is a deposit you’re getting credit for. If the deposits beat the bill, you get the difference back. If they fall short, you pay it.
That last step is the one the tax refund calculator handles. Put in your employment income, the tax withheld on your T4 and any deductions, and it tells you if you’re getting money back or owing. For a wider look at the steps, see our guide to tax returns in Canada.
Where does each number come from?
| What you need | Where to find it |
|---|---|
| Employment income | T4 slip, income box |
| Income tax already withheld | T4 slip, income tax deducted box |
| Interest, rent, other income | T5 slips, bank statements, your own records |
| RRSP and other deductions | Contribution receipts |
| Instalments paid | Your CRA account or payment records |
Collect every slip before you start. A missing one is the usual reason an estimate and the final assessment don’t agree.
What does a deduction do to the answer?
Begin with the plain case. On $75,000 of pay in Ontario with $14,000 withheld, tax for the year is $12,704.65, taxable income is $74,273, and you get $1,295.35 back.
Now claim a $5,000 RRSP contribution. Taxable income drops to $69,273, tax drops to $11,072.15 and the refund grows to $2,927.85. That’s $1,632.50 more, or about 33 cents for every dollar you deducted. Not bad for a receipt.
Flip it around. Add $5,000 of interest or rent and tax climbs to $14,187.15. You now owe $187.15, because the same $14,000 of withholding no longer covers the bill.
Why is a deduction worth so much?
Your last dollars of income are taxed above your average rate, so that’s where a deduction bites. The marginal tax rate calculator gives the rate on extra pay, interest, capital gains and dividends. If you’d rather see the whole bill first, the income tax calculator shows federal and Ontario tax, CPP and EI, and what’s left.
Credits are the other lever. The tax credits calculator shows what medical costs, tuition, donations or the age amount save you.
Habits that make the sum easier
Keep one folder for the year, paper or digital, and drop each slip and receipt in as it arrives. Come February, everything the calculator asks for is in one place.
Run the estimate twice, once in autumn and again when the slips land. The autumn run still leaves time to make an RRSP contribution or set cash aside for a bill. And if you expect to owe more than a small amount every year, the tax instalments calculator shows how to spread it out.
What trips people up?
- Using the wrong withholding figure. You want tax deducted for the whole year, not one pay period.
- Leaving out side income. Interest, rent and freelance pay count as income, slip or no slip.
- Expecting the estimate to match the notice of assessment. The tool doesn’t include every credit, benefit or claim.
- Forgetting the due date. Any balance is due April 30, even for self-employed people who file by June 15.
The estimate counts the basic personal amount, the employment amount and credits for CPP and EI. It leaves out refundable credits and benefits, so a real refund can come in higher.
What if the sum says you owe, and you can’t pay it all?
File anyway, and on time. The CRA’s 2026 tax tip for self-employed filers reminds people that a later filing date doesn’t move the payment date: any balance owing for 2025 was still due by April 30, 2026. The same page says the CRA can work with you on a payment arrangement, so call or sign in to your account before the balance gets older.
Take the $187.15 owing example above. It’s small enough that most people just pay it, but it shows why a little interest income can flip a refund into a bill, and why running the numbers in October beats finding out in April.
Our sources
Tax brackets, basic amounts and CPP and EI limits are the 2026 federal and Ontario figures from Canada Revenue Agency and Ontario government publications, checked in September 2026. Filing dates come from the CRA important dates page. This site isn’t affiliated with any government body. We rechecked the filing and payment dates on the CRA’s filing dates page in November 2026.
Frequently asked questions
Will I get a refund?
Subtract your tax for the year from the tax already withheld. If withholding is higher, the difference comes back to you as a refund, and if it is lower you owe the balance. On $75,000 of employment income in Ontario with $14,000 withheld, our example gives a refund of $1,295.35.
Which numbers do I need?
Employment income and tax deducted from your T4, any other income from T5 or T3 slips, deductions such as RRSP contributions, and any instalments you paid. Your notice of assessment from last year also helps, because it shows your RRSP room and carried-forward amounts.
How much does an RRSP deduction change things?
On $75,000 of pay in Ontario, a $5,000 RRSP deduction lifts the refund from $1,295.35 to $2,927.85. That is $1,632.50 more back for $5,000 put in, because the deduction lowers taxable income at your marginal rate, federal and Ontario together.
Can extra income leave me owing?
Yes. Add $5,000 of other income, such as interest or a side job with no tax withheld, and the same example turns from a refund into a balance owing of $187.15. Income without withholding is the most common reason people who usually get a refund end up owing.
When do I have to pay a balance?
By April 30 for most people. Self-employed filers can file by June 15, but any tax owing is still due April 30, and interest runs from that date. For the 2025 return those dates were April 30, 2026 and June 15, 2026, and the 2026 dates usually fall on the same days in 2027.
- How to file your tax return in Canada: steps and dates
What to gather, when your return is due and how to file in Canada, from the first slip to the notice of assessment that closes the year