Many people don’t fully understand the difference between marginal and effective tax rates, which often leads them to incorrect conclusions. News stories almost always discuss the marginal tax rate — the rate one pays on each additional dollar of income. For example:
WASHINGTON — Prospects improved for a major overhaul of the federal estate tax, as key senators moved toward compromise yesterday, and Senate Majority Leader Bill Frist, with one eye on the November elections, said he wants to settle the issue this year.
The likely basis for discussions of a deal would be a proposal unveiled by Sen. Jon Kyl (R., Ariz.) that would exempt the first $5 million of a person’s estate, or $10 million per couple. The remainder would be taxed at two rates. Estates valued at less than $30 million would be taxed at the capital gains rate, currently 15%; anything over $30 million faces a 30% tax.
Republicans enacted a law in 2001 to temporarily phase out the tax. Under current law, $2 million worth of an estate is exempted from the tax, and the remainder is taxed at rates as high as 46%. In 2011, the law expires and the rate snaps back to 55%.
Mullins, Brody. “Estate-Tax Overhaul Gains Ground” The Wall Street Journal. 8 June 2006.
Based on these numbers, one might conclude that while the proposal significantly reduces the tax rate, it doesn’t even cut the top rate in half, so revenues from the estate tax should still be at least half what they were before. This conclusion is, however, almost certainly incorrect. The problem is that marginal tax rates aren’t directly comparable due to the presence of deductions and tax brackets. The effective tax rate — total taxes paid divided by tax base (e.g. income or estate size) — should always be used for comparisons, either on an individual or group basis.
To better illustrate how the two can diverge, consider the following calculation of effective tax rates based on estate size E:
| 2006 Law |
| Estate Size |
Marginal Tax Rate |
Effective Tax Rate |
| <= $2,000,000 |
0 |
0 |
| > $2,000,000 |
46% |
(0.46*E - 920,000)/E |
| Kyl’s Proposal |
| Estate Size |
Marginal Tax Rate |
Effective Tax Rate |
| <= $5,000,000 |
0 |
0 |
> $5,000,000 <= $10,000,000 |
15% |
(0.15*E - 750,000)/E |
| > $10,000,000 |
30% |
(0.30*E - 2,250,000)/E |
Or, graphically:
As the estate size increases, the effective tax rate asymptotically approaches the top marginal tax rate, and the decrease in effective tax rate approaches the original assumption. However, there is a significant portion of the graph where the drop in effective estate tax rate is far more than 50%. Consider, for example, the drop in effective estate tax rate from 36.8% to 7.5% for estates of size $10 million.
Therefore, depending on the size of the average American estate, the cost to the Treasury of Kyl’s proposal may be far more than one might naïvely presume, due to the divergence of marginal and effective tax rates.
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