Horizontal Equity
What is Horizontal Equity?
Horizontal equity is the tax principle that people in the same economic circumstances should pay the same amount of tax.
Horizontal equity is one half of the ability-to-pay approach to tax fairness: equals should be treated equally, while vertical equity handles the other half, that those with greater ability to pay should bear more. It does most of its practical work as a test of tax preferences, since every deduction, exclusion or credit available to one household but not to an otherwise identical one breaks equal treatment and simultaneously tilts behavior toward the favored activity. The principle is harder to apply than it sounds because it needs a workable definition of the same circumstances, and annual income is a poor one: two households with identical income can differ in family size, medical costs, hours worked, whether their earnings are steady or volatile, and whether the income is wages or capital gains. Some economists argue that the principle has no independent content, on the grounds that any consistent rule linking ability to tax liability already treats equals equally. It survives anyway because it is the cleanest language available for criticizing a loophole.
Horizontal Equity: a worked example
Two households each earn $80,000. Suppose a flat 22 percent rate applies to taxable income, the standard deduction is $15,000, and one household rents while the other owns a home and itemizes $28,000 of mortgage interest and property tax. The renter has taxable income of $80,000 - $15,000 = $65,000 and owes 0.22 x $65,000 = $14,300, an effective rate on gross income of 14,300 / 80,000 = about 17.9 percent. The homeowner has taxable income of $80,000 - $28,000 = $52,000 and owes 0.22 x $52,000 = $11,440, an effective rate of 11,440 / 80,000 = 14.3 percent. Two households with the same income face bills that differ by $2,860 and effective rates about 3.6 percentage points apart, so the deduction is a measurable violation of horizontal equity.
The mistake students make with horizontal equity
Students say a progressive income tax achieves horizontal equity, because progressivity is the fairness idea they were taught first. Progressivity is about vertical equity, meaning how the burden changes as ability to pay changes. Horizontal equity is only about people who are alike, so a flat tax with no deductions satisfies it completely while doing little for vertical equity, and a steeply graduated tax full of targeted breaks can be strong on vertical equity and weak on horizontal equity. The two standards are independent, and a tax system can pass either one while failing the other.
Horizontal Equity questions
What is the difference between horizontal and vertical equity?
Horizontal equity says taxpayers in the same situation should pay the same amount, while vertical equity says taxpayers with greater ability to pay should bear a larger burden. Both come out of the ability-to-pay principle, but they answer different questions, one about equals and one about unequals. A system can satisfy one and fail the other, which is why economists evaluate tax proposals against both rather than treating fairness as a single dimension.
Why is horizontal equity hard to achieve in practice?
Because the same circumstances has to be measured with something, and the usual measure, annual income, hides real differences in ability to pay such as family size, medical expenses, unpaid work at home, and whether earnings are steady or swing between good and bad years. Under a graduated rate schedule the volatile earner pays more over a lifetime than the steady earner with the same lifetime income. Tax preferences then add further differences on purpose, so every exclusion, deduction and credit that only some taxpayers can claim widens the gap between equals.
Does the benefits principle conflict with horizontal equity?
It can, because the benefits principle charges people according to the government services they use rather than according to their ability to pay. Two equally well-off households owe the same under the ability-to-pay standard, but the one that drives more pays more fuel tax under the benefits principle. Most tax systems use both ideas in different places, funding roads through user charges while funding schools and defense from general taxation, and the tension between them is a normative disagreement rather than a mistake.
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