WealthQuebec real marginal tax rate curve: visualizing the "Laferrière curve"
In Quebec, earning one more dollar doesn't always increase your net income by that much. At certain income levels, the gradual phase-out of tax credits and benefits (the Quebec Allocation famille, the Canada Child Benefit) stacks on top of regular income tax and pushes the real marginal tax rate — sometimes past 50-60% — well above the posted tax bracket rate. This is a well-documented phenomenon in Quebec tax policy, sometimes called the "Laferrière curve" or the effective marginal tax rate curve. The tool below lets you visualize this curve for a simple household profile.
Calculator inputs
Known simplifications: this chart models federal and Quebec provincial income tax (2026 brackets), the Quebec Allocation famille reduction (4% of net family income above the threshold), and the Canada Child Benefit reduction (federal tiered rates by number of children). It does not include the Quebec solidarity tax credit, the GST/HST credit, or other provincial/federal credits which, in reality, would push the "bumps" on this chart even higher. The Canada Child Benefit reduction rates used here are an approximation of the CRA's standard structure — consult the official CRA benefits calculator for an exact amount.
How to read the curve
The horizontal axis represents gross household income, from $10,000 to $120,000, in $2,000 increments. The vertical axis represents the real marginal tax rate: the share of one additional dollar earned that disappears to combined income tax and benefit reductions. When the curve climbs then drops sharply, it signals that a benefit phase-out zone (Allocation famille or CCB) has just been exhausted — the household has "finished losing" that benefit, so the real marginal rate falls back to the base tax rate.
Worked example
Take a couple with 2 children and a gross household income of $65,000. The combined federal + Quebec marginal rate at this income level is about 39.5% (14% + 20.5% federal depending on the bracket, 19% provincial). But at $65,000, this household is also in the Quebec Allocation famille reduction zone (above the $59,369 threshold for a couple, 4% reduction) and in the first Canada Child Benefit reduction tier for 2 children (approximately 13.5% between $38,237 and $82,847 of adjusted family net income). The approximate real marginal rate becomes roughly 39.5% + 4% + 13.5% = 57% — well above the rate shown in the tax brackets alone. And this calculation still excludes the solidarity tax credit and GST credit, which would push this figure even higher for many households.
Why this curve exists
Income support programs (Allocation famille, Canada Child Benefit, solidarity tax credit, etc.) are designed to target low- and middle-income households. To do this, they gradually decrease as income rises. The problem is that several of these reductions overlap in certain income ranges, creating a cumulative effect that tax tables alone don't show. This is a real, well-documented phenomenon among Quebec tax specialists, often illustrated by a bumpy curve — hence the name "Laferrière curve" or effective marginal tax rate curve, popularized in comparative tax analyses in Quebec.
Frequently asked questions
What exactly is the Laferrière curve?
It's a visual representation of the real marginal tax rate — income tax combined with the loss of benefits and credits — at different income levels. It's a well-known concept in Quebec tax policy used to illustrate that the "posted" tax rate in the brackets doesn't tell the whole story for households receiving income-tested benefits.
Does this calculator give me my exact real marginal rate?
No. This tool is a simplified educational visualization. It does not account for every credit (the solidarity tax credit, GST/HST credit, additional provincial credits, etc.) or your full tax situation. For an accurate calculation of your own situation, consult a CPA or financial planner, and use the official CRA calculator for the Canada Child Benefit.
Why does the real marginal rate drop after climbing?
Because benefits like the Allocation famille or the Canada Child Benefit eventually phase out completely at a certain income level. Once there's no more benefit left to reduce, the marginal rate falls back to the base tax rate (federal + provincial), without the "bump" caused by the benefit reduction.
Does this phenomenon affect all Quebec households?
No — it mainly affects households with children whose family income falls within the benefit reduction zones (roughly $38,000 to $130,000 depending on the number of children and family situation). Households without children, or at very low or very high income, see an effect much closer to the posted marginal tax rate alone.
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