Marginal Tax Rate vs Earned Income Tax Credit
Marginal Tax Rate and Earned Income Tax Credit are two Public Finance & Taxation concepts in AP Economics that students often mix up. The marginal tax rate is the tax rate applied to the next dollar of income earned. The Earned Income Tax Credit is a refundable tax credit for low- and moderate-income workers that rises with earnings, then plateaus, then phases out. Here is how they compare side by side.
In a progressive system it is the rate of your top bracket. It drives incentives to work and invest because it determines how much of additional income you keep. It is usually higher than the average tax rate.
The credit is calculated from wage or self-employment income, so a household with no earnings receives nothing; the design rewards work rather than replacing it. In the phase-in range each extra dollar earned raises the credit, which acts like a wage subsidy and pulls people into the labor force. The credit then holds flat over a plateau and falls as income rises further, so households in the phase-out range face a higher effective marginal tax rate. Because it is refundable, a family whose credit exceeds its income tax liability receives the difference as a payment. It is not a deduction: a deduction shrinks taxable income, while this credit reduces tax owed dollar for dollar and can go below zero.
Marginal Tax Rate vs the EITC: The Statutory Rate Against the Rate You Actually Face
| Marginal Tax Rate | Earned Income Tax Credit | |
|---|---|---|
| What the number describes | The rate the schedule charges on the next dollar | A refundable credit whose size depends on how much is earned |
| Shape as earnings rise | Steps up at each threshold and never steps down | Rises, flattens, then falls back to zero |
| What it does to the next dollar | Takes a fixed share of it | Adds to it during the phase-in, claws back during the phase-out |
| Statutory or effective | The statutory figure printed in the schedule | Moves the effective rate without changing any statutory rate |
| Sign it can take | Positive, since a rate applies to income earned | Can drive the effective rate negative, so an extra dollar leaves more than a dollar |
| Which decision it moves | Hours and effort, given that someone already works | Mainly the decision to work at all, since the phase-in rewards entry |
| Where it appears on a return | In the rate applied to taxable income | After the tax is computed, paid out in cash when it exceeds the bill |
One statutory rate, three different prices on the next dollar
Build a hypothetical credit with the usual three-part shape. It pays 40 cents for every dollar earned up to 30,000, so it peaks at 12,000. It holds at 12,000 from 30,000 to 36,000. Above 36,000 it falls by 20 cents per extra dollar, reaching zero at 96,000. Put a flat statutory income tax rate of 10 percent beside it so the credit is the only thing moving. In the phase-in range, an extra dollar of wages costs 10 cents in tax and brings 40 cents of credit, leaving the household 30 cents better off than the dollar itself: an effective marginal rate of negative 30 percent. On the plateau the credit does not move, so the effective rate is the statutory 10 percent. In the phase-out range the extra dollar costs 10 cents in tax and destroys 20 cents of credit, an effective rate of 30 percent. The statutory rate was 10 percent at every income in that walk. The rate governing whether an extra hour is worth working ran from negative 30 to positive 30, a swing of 60 points that no bracket table anywhere records.
The two halves of the credit pull labor supply in opposite directions
The phase-in and the phase-out are not two views of one incentive. They push different decisions different ways. The phase-in raises the reward for taking a job at all, since the first hours of work carry a subsidy on top of the wage, and that participation margin is where the evidence for earnings credits is strongest. The phase-out lowers the reward for working more hours once someone is already employed, and for a second earner it can lower the reward for taking a job at all, because the household's first earner has already carried the credit into the clawback range. Designers cannot buy their way out of the trade-off. A larger maximum has to be withdrawn somewhere, so raising it either steepens the clawback or spreads it across more households. What they can choose is which margin to protect. Compare an unconditional payment, which has no phase-in and no phase-out and so leaves the marginal rate alone at every income while costing far more to deliver: see /glossary/negative-income-tax.
Frequently asked questions
Can an effective marginal tax rate be negative?
A negative effective marginal tax rate appears in the phase-in range of an earnings credit, where the next dollar of wages brings in more credit than it costs in tax. With a credit paying 40 cents per dollar earned and a statutory rate of 10 percent, the household ends up 30 cents better off than the extra dollar itself, an effective rate of negative 30 percent. No statutory rate in the code is negative, and the sign comes entirely from a credit that grows with earnings.
Why does the EITC phase-out act like a tax increase?
Losing 20 cents of credit for every extra dollar earned costs a household exactly what a 20 percentage point rate rise would cost, so the clawback stacks on whatever the statutory schedule already charges. In the example above, a statutory rate of 10 percent plus a 20 cent clawback gives an effective marginal rate of 30 percent, which is why earnings of 60,000 leave the household only 7,000 better off than earnings of 50,000 despite the extra 10,000 earned.
Would a larger credit improve work incentives?
A larger maximum credit strengthens the reward for entering work and weakens the reward for working more, because the extra money has to be withdrawn somewhere. Raising the maximum from 12,000 to 16,000 while keeping a 20 cent clawback stretches the phase-out across 80,000 of earnings instead of 60,000, so many more households sit in the range where an extra dollar is worth 70 cents. The design question is which margin matters more, not how generous the headline number looks.
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