Proportional Tax

A proportional tax is a tax whose rate stays constant as its base rises or falls, so the tax paid moves in fixed proportion to the base. Double the base and the tax doubles while the percentage does not move, which is the same as saying the average rate, total tax divided by the base, equals the marginal rate, the rate charged on the next dollar of base, at every level. Proportional names one property of a charge, the behavior of its rate, and says nothing about who bears it or what it funds.

Proportional, Progressive, and Regressive Rates

All three labels answer one question: what the rate does as the base gets bigger. A proportional rate holds still. A progressive rate climbs, so a larger base is taxed at a higher percentage than a smaller one and the average rate rises behind the marginal rate. A regressive rate falls, so a larger base is taxed at a lower percentage than a smaller one.

Each label reads a rate structure against a stated measure, so name the measure before you use one of them. The same charge can be proportional against the amount it is actually levied on and something else entirely against a broader measure such as total income.

Where Proportional Rates Show Up in the Code

The Hospital Insurance Tax Is the Cleanest Example

The Code imposes on the income of every individual a tax equal to 1.45 percent of the wages received with respect to employment, for hospital insurance (26 U.S.C. 3101(b)(1)). No bracket sits above that rate, and no cap cuts the base off (26 U.S.C. 3121(a)(1)). The rest of the Federal Insurance Contributions Act (FICA) mechanics, including the capped side and the employer’s own charge, sit in payroll tax.

One boundary matters. Above a wage threshold the employee’s Medicare charge picks up a further 0.9 percent as Additional Medicare Tax (26 U.S.C. 3101(b)(2)), so the employee side stops being proportional at that point even though the 1.45 percent rate itself never changes. The thresholds and the rest of that charge are set out in Medicare tax.

Backup Withholding Borrows Its Rate From a Graduated Schedule

Section 3406(a)(1) lists four triggers, among them a payee who fails to furnish a taxpayer identification number in the manner required, and a notice from the Secretary to the payor that the number furnished by the payee is incorrect. On a reportable payment, if any of the four applies, the payor must deduct and withhold from the payment a tax equal to the product of the fourth lowest rate of tax applicable under section 1(c) and that payment (26 U.S.C. 3406(a)(1)). The statute states no percentage of its own.

The IRS gives the current rate as 24 percent (IRS, Backup Withholding). Once that figure is fixed for the year it applies to every reportable payment at the same percentage, however large the payment, which is what makes the charge proportional on its base even though the rate was lifted out of a graduated table.

That withholding is not a final charge on the payee. Section 3406 sits in chapter 24, and the amount withheld as tax under that chapter is allowed to the recipient of the income as a credit against the income tax imposed by subtitle A (26 U.S.C. 31(a)(1)). The constant rate sits on the withholding, not on what the payee finally owes, so the measure has to be named here as well.

The Net Investment Income Tax Is Flat on a Gated Base

For an individual the Code imposes a tax equal to 3.8 percent of the lesser of net investment income for the year or the excess of modified adjusted gross income over the threshold amount (26 U.S.C. 1411(a)(1)), with the thresholds themselves laid out in Medicare tax. The rate never moves, so the charge is proportional on the base it reaches, but that base only exists above the threshold. Flat on its own base and flat on income are two different statements, and this one is the first without being the second.

The Federal Individual Income Tax Is Not Proportional

Section 1 imposes the individual tax through rate tables in which the percentage rises as taxable income rises, both in the original tables and in the tables substituted for years beginning after 2017 (26 U.S.C. 1(a) and 1(j)(2)). A C corporation is the contrasting case: the tax section 11 imposes on corporate taxable income is a single 21 percent (26 U.S.C. 11(b)). Which return carries which liability is traced in federal income tax liability.

A Worked Example on Two Different Bases

Say two employees are paid annual wages that both sit below every Additional Medicare Tax threshold, one of them at twice the other’s level, and the only charge in view is the employee hospital insurance tax.

Rate                                     1.45%

Employee A
  wages                               60,000.00
  hospital insurance tax                 870.00
  average rate      870 / 60,000           1.45%

Employee B
  wages                              120,000.00
  hospital insurance tax               1,740.00
  average rate    1,740 / 120,000          1.45%

The second base is twice the first and the tax is twice as large, so the average rate is identical at both levels. That identity is the entire content of the word proportional.

What Proportional Tax Gets Confused With

Proportional Tax and Flat Tax

In ordinary use the two are one word: a single rate applied across the base. They come apart when flat tax names a whole system rather than a single charge, because single-rate system designs commonly exempt an amount at the bottom before the rate applies. A rate charged only on the part of the base above an exempt amount still leaves an average rate that climbs, since the exempt slice is a shrinking share of a growing base. One marginal rate is not by itself proof of a constant average rate.

A Proportional Rate and a Regressive Burden

These are claims about two different denominators, and both can be true of one charge at once. A tax with a constant rate on its own base is proportional measured against that base. Calling the same tax regressive usually measures it against total income instead, and if the base is a smaller share of income at higher incomes then the charge takes a falling share of income while its stated rate never moves. Neither label means much until the measure behind it is stated.

Proportional to the Price

The European Union’s VAT Directive describes value added tax as a general tax on consumption exactly proportional to the price of the goods and services (Council Directive 2006/112/EC, Article 1(2)). That phrase does a different job. It says the charge tracks the price of the transaction however many stages the goods pass through, not that one rate applies to a person’s income. The mechanism it describes is worked through in value added tax.

Common Questions

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