marginal vs average tax rate

When people ask 'what tax rate do you pay?' they are really asking two different questions and usually only get one answer. The marginal tax rate is the rate on your NEXT dollar earned — if you got a small raise, what fraction of it would the taxman take? The average tax rate is the rate on ALL your income — your total tax bill divided by your total income. In a progressive system these two numbers are different, and confusing them causes endless misunderstanding.

Here is the difference made concrete. Suppose income up to 20,000 is taxed at 10 percent, 20,000–50,000 at 20 percent, and above 50,000 at 40 percent, and you earn 60,000. Your marginal rate is 40 percent — that is what applies to your last (60,000th) dollar and to your next raise. But your total tax is 2,000 + 6,000 + 4,000 = 12,000, so your average rate is 12,000 / 60,000 = 20 percent. The average rate is always lower than the top marginal rate in a progressive system, because the lower brackets pull it down. The marginal rate drives decisions ('is it worth working extra hours?'); the average rate measures the overall burden you actually carry.

This distinction is one of the most practically important in all of tax. Decisions at the margin — whether to take overtime, accept a bonus, or have a second earner in the household work more — depend on the marginal rate, not the average, because they concern the next dollar. Meanwhile, the average (or 'effective') rate is the honest measure of how much of your income the state actually takes, and it is what you should compare across people or countries. The popular fear that 'a raise can leave me worse off' confuses the two: a higher marginal rate on extra income never makes your total take-home fall.