Quick answer
Two T4 jobs usually leave you owing money at filing, because each employer withholds as if its paycheque were your only income, so your combined pay is taxed at a higher stacked rate once you file. In the calculator's own $70,000-plus-$30,000 Ontario example, with the basic personal amount claimed at one job only, that gap is about $3,479, partly offset by a $1,376.05 automatic CPP/EI refund, for a net roughly $2,103 owing.
Why two T4 jobs can leave you owing money
Having two jobs at once is common — a full-time role plus weekend shift work, a day job plus a part-time gig — and it creates a tax problem that surprises a lot of people the first time it happens: you end up owing money at filing even though tax was withheld from every single paycheque. The cause isn't fraud or a payroll mistake. It's that each employer's payroll system does exactly what CRA's own T4127 payroll formulas tell it to do: treat the income it pays you as though it were your entire income for the year. Neither employer knows the other one exists. Canada's federal and provincial tax brackets are progressive — each additional dollar of income can be taxed at a higher rate than the last — so the tax on $100,000 earned from one job is genuinely more than the tax on two $50,000 jobs calculated separately and added together. When you file your return, CRA combines both T4 slips and taxes the true, stacked total. The difference between that true amount and what the two employers withheld separately becomes a balance due.
Calculated tax = Tax(Job 1 income + Job 2 income, combined)
Gap at filing = Calculated tax − Total withheld (almost always positive with two ordinary T4 jobs)
How each employer decides how much to withhold: the TD1 form
Every new employee fills out a federal TD1, Personal Tax Credits Return, plus a provincial or territorial version. Line 13 is the total claim amount — normally the basic personal amount, $16,452 federally for 2026 — and whatever number sits there tells payroll how big a tax credit to apply before withholding anything. The TD1 form itself addresses the two-job case directly, under the heading "More than one employer or payer at the same time": if you already claimed your personal amounts on another TD1 for the year, you're instructed to check that box, write "0" on line 13, and leave lines 2 to 12 blank at every other job. Your provincial or territorial form works the same way and has to be filled in as well: Ontario's TD1ON has its own “More than one employer or payer at the same time” box and asks for 0 on line 10, and Quebec's TP-1015.3-V says to go to line 10 and enter 0. This calculator removes both basic personal amounts at Job 2, so if you change only the federal form the employer still credits the provincial one: on a $30,000 second job that is $655.94 less Ontario tax withheld than the worked example below shows (5.05% of Ontario's $12,989 basic amount), or $2,653.28 less in Quebec (14% of $18,952). The sensible default — and this calculator's own default — is claiming the basic personal amount on both forms at exactly one job (typically the one you expect to pay you more over the year) and claiming nothing at any other. That single choice is doing real work: a $0 claim at Job 2 means that employer withholds meaningfully more than it otherwise would, partly (not fully) offsetting the bracket-stacking problem above.
The basic personal amount: claim it once, not twice
Nothing on a TD1 form technically stops you from writing $16,452 on line 13 at a second job too — the form just tells you not to, and plenty of people miss that instruction or fill out a generic form without reading page 2. The consequence is the shortfall gets substantially worse, not better: now neither employer is doing the extra withholding the "more than one employer" box exists to trigger. Toggle the checkbox in this calculator to see the difference for yourself — in the worked example below, correctly claiming the amount once leaves roughly $3,479 owing at filing, while claiming it at both jobs pushes that to roughly $6,438. It feels like it should help (more credits, less tax each paycheque) but it only defers the bill to April, with a bigger number attached.
CPP and EI: the other kind of over-contribution
There's a second, less-discussed effect, and it does not simply run in your favour. CPP (QPP in Quebec) and EI aren't calculated from your TD1 claim at all; each employer works them out purely from the income it pays you, independently applying the same annual rules: a $3,500 basic exemption before CPP starts, a hard stop at the $74,600 Year's Maximum Pensionable Earnings for CPP's base tier (with a second 4% tier, CPP2, running up to $85,000), and a hard stop at $68,900 for EI. CRA's employer guide says the annual maximum applies to each job an employee holds with different employers. Two employers therefore apply two $3,500 exemptions, and that makes you contribute less CPP than the true figure, by up to $208.25 (5.95% of $3,500): CRA's line 30800 page warns that you may have contributed less than the required amount if you had more than one employer. The overpayment comes from the ceilings. With neither job alone above $74,600, the base tier overshoots once your combined pay passes $78,100 (the ceiling plus the second exemption), but CPP2, which each employer withholds only on its own pay above $74,600, is then short by up to $416, so the CPP figure this page shows, which nets the two the way Schedule 8 does, becomes an overpayment only from about $85,092 of combined pay. (QPP's rate is 6.30%, so in Quebec the two exemptions leave you up to $220.50 short and the netted QPP figure becomes an overpayment from about $84,187.) EI has no exemption: with both jobs under $68,900 its overpayment starts the moment combined pay passes $68,900, and if one job is already above it, every EI dollar withheld at the other is overpaid. When there is an excess you claim it on your return, a CPP overpayment on line 44800 and an EI overpayment on line 45000, and CRA refunds it or uses it against tax you owe. Quebec residents do not use line 44800: the QPP and QPIP overpayments are claimed on the Revenu Québec return (lines 452 and 457), and only the EI part is CRA's. The refund doesn't cancel out the income-tax shortfall (they're different lines on the same return, taxed and credited independently), but it does soften the net amount you actually have to pay.
Worked example — $70,000 and $30,000 in Ontario
An Ontario resident earns $70,000 at their main job (basic personal amount claimed there) and $30,000 at a second job (federal TD1 and provincial form both correctly set to claim $0, box checked).
- Job 1 withheld: computed exactly like a single $70,000 salary — federal tax $7,278.19 plus Ontario tax $3,855.73 (including the $600 Health Premium) = $11,133.91, the same engine and method as our Take-Home Pay Calculator.
- Job 2 withheld (claim code 0): $30,000 taxed with no federal or provincial basic personal amount at all — only the Canada Employment Amount and the CPP and EI credits survive, because T4127 applies those to every employee regardless of the claim code. Federal tax $3,700.66 plus Ontario tax $1,710.68 (a flat $300 Health Premium) = $5,411.33. Notice this is a steep 18.0% average rate on a modest $30,000 — that's the visible cost of the "more than one employer" box, and a common source of "why is my second job taxed so much?" confusion.
- Total withheld: $11,133.91 + $5,411.33 = $16,545.25.
- Calculated tax on the combined $100,000: federal tax $13,301.60 plus Ontario tax $6,722.75 (which now includes a small $25.79 surtax and the $750 Health Premium tier) = $20,024.35.
- Gap at filing: $20,024.35 − $16,545.25 ≈ $3,479 owing — even though both employers withheld tax correctly by their own rules, and the TD1 forms were filled out the right way.
- Marginal rate on the second job's dollars: since Job 2's income sits on top of Job 1's in the true calculation, its last dollars are taxed at the combined marginal rate of 31.48% (20.5% federal + 9.15% Ontario × the surtax multiplier) — well above either job's own bracket in isolation.
- CPP and EI overpayment: each job's own CPP comes to $3,956.75 and $1,576.75 (total $5,533.50), against a true combined CPP of $4,646.45 — an $887.05 overpayment. EI comes to $1,123.07 and $489.00 (total $1,612.07) against a true combined EI of $1,123.07 (Job 1 alone already exceeds the $68,900 cap) — a further $489.00 overpayment. Together, $1,376.05 is refunded automatically at filing.
- Net effect: $3,479 owing on the income-tax side, less $1,376.05 refunded on the CPP/EI side, leaves roughly $2,103 as the real net amount to plan for.
Figures above are rounded to the cent at each step for readability; the calculator itself carries full precision throughout, so its result can differ from this worked example by a few cents.
How to fix it before it happens again
The TD1 form has a line built for exactly this problem: "Additional tax to be deducted" on page 2, where you write in a fixed extra dollar amount you want withheld from every payment at a given job. Divide this calculator's gap figure by however many pay periods you have left in the year for a rough starting number, hand the updated TD1 to your employer's payroll department, and it applies to your next paycheque onward (not retroactively). CRA's own Payroll Deductions Online Calculator (PDOC) can help you land on a more precise figure for your actual pay frequency. The opposite request — asking for less tax withheld because of RRSP contributions or other credits — needs a completed Form T1213 and a letter of authority instead; that's a different form for a different problem, and not what applies here. One more thing worth knowing: CRA lists income from more than one job among the reasons to pay tax by instalments. If your net tax owing (the income-tax gap above, without CPP or EI) is more than $3,000 and was also more than that in 2025 or 2024, quarterly instalments are due. This calculator's starting gap of about $3,479 is over $3,000, but whether you owe instalments depends on your earlier years, which it cannot see. In Quebec the line is $1,800 and there are two separate tests, CRA's on the federal part of the gap and Revenu Québec's on the Quebec part; this calculator shows the two parts added together, so a Quebec gap over $1,800 does not by itself meet either test.
What this calculator doesn't model
This tool assumes both incomes are ordinary T4 employment income with tax withheld at source, in the same province, for the full year, with no RRSP contribution, and a TD1 that claims only the basic personal amount at Job 1 (no spouse, dependant, disability, tuition or age amounts). It doesn't model a third job or more (the same bracket-stacking logic just keeps compounding), income that starts or changes partway through the year, or self-employment or freelance income (which has no payroll withholding at all — see the FAQ). CPP2 (the second CPP tier, on income between $74,600 and $85,000) is withheld by each employer only on its own pay above $74,600; when neither job alone reaches that line but your combined income does, no employer withholds any CPP2 at all, and the calculator nets that shortfall against the base-tier overpayment in the CPP figure it shows rather than listing the two separately. When that CPP figure is a shortfall rather than an overpayment (Ontario $40,000 and $30,000, for example), CRA limits the base CPP credit and the enhanced-CPP deduction to what was actually withheld (Schedule 8, Part 3b); this page's calculated tax assumes the full required amount, so it is a little low in that case, by $43.38 in that example.
FAQ
Why do I owe money at tax time if both my employers were withholding tax?
Because each employer withholds tax as though their paycheque were your only income for the year. Canada's tax brackets are progressive, so tax on $100,000 from one job is more than tax on two $50,000 jobs added together — the second $50,000 gets taxed at your top bracket in the correct calculation, but each employer's payroll software starts counting from the bottom bracket again, since neither one knows about the other job. The gap between what was actually withheld and what you truly owe on your combined income becomes a balance due when you file.
What does the "more than one employer or payer" box on the TD1 form actually do?
It tells that employer not to give you a second basic personal amount tax credit. CRA's TD1 form says it directly: if you have more than one employer at the same time and already claimed personal tax credit amounts on another TD1, check this box, enter "0" on Line 13, and don't fill in lines 2 to 12. Your provincial form needs the same treatment, because it carries its own basic personal amount: Ontario's TD1ON has its own box and asks for 0 on line 10, and Quebec's TP-1015.3-V says to go to line 10 and enter 0. An employer with no provincial form uses the province's basic personal amount, so changing only the federal form leaves the provincial credit in place: on a $30,000 second job, Job 2 would withhold $655.94 less Ontario tax than this calculator shows (5.05% of Ontario's $12,989 basic amount) or, in Quebec, $2,653.28 less (14% of $18,952). In practice this means your main job's forms claim the normal basic personal amounts, $16,452 federally, and every other job's forms claim nothing — so each of those jobs withholds more tax than it otherwise would, partly compensating for the bracket-stacking problem above, though usually not all the way.
What happens if I accidentally claim the basic personal amount at both jobs?
The shortfall gets meaningfully worse, because now neither employer is withholding the extra amount that the "more than one employer" box exists to collect. In this calculator's own worked example — $70,000 and $30,000 in Ontario — correctly claiming the basic personal amount at only one job leaves about $3,479 owing at filing; claiming it at both jobs pushes that gap to about $6,438. It's an easy mistake to make, since nothing stops you from writing a claim amount on a second TD1 — the form just tells you not to.
Why did I overpay CPP and EI, and how do I get it back?
Each employer calculates your CPP (or QPP in Quebec) and EI deductions using only the income they pay you, stopping once your earnings at that job reach the annual ceiling — $74,600 for CPP's base tier and $68,900 for EI in 2026. With two jobs, each employer applies its own $3,500 CPP exemption and its own ceilings independently. The two exemptions alone make you contribute less CPP than the true figure, by up to $208.25 (5.95% of $3,500), as CRA's line 30800 page warns for anyone with more than one employer. The overpayment comes from the separate ceilings: once your combined pay is well past them, the two employers together have deducted more than the true annual maximum even though neither did anything wrong. You claim the excess on your return: a CPP overpayment on line 44800 and an EI overpayment on line 45000, which CRA refunds or applies against tax you owe. Quebec residents do not use line 44800; they claim a QPP or QPIP overpayment on their Quebec return (TP-1 lines 452 and 457), and only the EI part goes on line 45000.
How do I stop this from happening again next year?
The TD1 form has a line for exactly this: "Additional tax to be deducted" on page 2, where you can ask either employer to withhold a fixed extra dollar amount from every payment. CRA's own Payroll Deductions Online Calculator (PDOC) can help you work out roughly how much, or you can use this calculator's gap figure divided by your remaining pay periods as a starting estimate. File the updated TD1 with your employer's payroll department — it takes effect on your next pay run, not retroactively. CRA also lists income from more than one job among the reasons to pay tax by instalments: if your net tax owing (income tax after what your employers withheld, without CPP or EI) is more than $3,000 and was also more than that in 2025 or 2024, quarterly instalments are due. The gap this calculator starts with, about $3,479, is over $3,000, but whether you owe instalments depends on your earlier years, which it cannot see. In Quebec the line is $1,800 and there are two separate tests, CRA's on federal tax and Revenu Québec's on Quebec income tax, while this calculator shows the two gaps added together.
Does this apply to freelance or self-employment income too?
No — this calculator assumes both incomes are T4 employment income with tax withheld at source, which is what creates the withholding gap in the first place. Self-employment and most freelance income has no payroll withholding at all; instead you're expected to pay quarterly tax instalments (or the full amount by the following April) based on your total income from every source, employment and self-employment combined. If one of your "jobs" is really freelance or contract work, see our Freelance Quote Calculator instead — the mechanism here doesn't apply.
What if I have three or more jobs?
The same thing happens with every extra employer: each one withholds as if its job were your only income. This calculator takes two incomes, so add your smaller jobs together in the second field. A third employer would start from the bottom bracket again and apply its own $1,501 Canada employment amount credit, so the real shortfall will be somewhat larger than the estimate you get that way.
Is a second job taxed at a higher rate?
No. There is no separate rate for a second job — every dollar of your combined income runs through the same federal and provincial brackets. It feels taxed more for two reasons: the second job’s earnings sit on top of your first job’s income, so they are taxed at your marginal rate rather than starting from zero, and the second employer withholds as if its pay were your only income, so too little comes off during the year and the difference lands at filing.
This page is general information based on published 2026 federal and provincial payroll formulas and CRA's TD1 guidance, not tax or financial advice. Your own return may differ — talk to a licensed accountant about your specific situation.