What if we taxed market share?

Apr 18 JDN 2459321

In one of his recent columns, Paul Krugman lays out the case for why corporate tax cuts have been so ineffective at reducing unemployment or increasing economic growth. The central insight is that only a small portion of corporate tax incidence actually seems to fall on real capital investment. First, most corporate tax avoidance is via accounting fictions, not real changes in production; second, most forms of investment and loan interest are tax-deductible; and the third is what I want to focus on today: Corporations today have enormous monopoly power, and taxing monopoly profits is Pigouvian; it doesn’t reduce efficiency, it actually increases it.

Of course, in our current system, we don’t directly tax monopoly profits. We tax profits in general, many—by some estimates, most—of which are monopoly (or oligopoly) profits. But some profits aren’t monopoly profits, while some monopolies are staggeringly powerful—and we’re taxing them all the same. (In fact, the really big monopolies seem to be especially good at avoiding taxes: I guarantee you pay a higher tax rate than Apple or Boeing.)

It’s difficult to precisely measure how much of a corporation’s profits are due to their monopoly power. But there is something that’s quite easy to measure that would be a good proxy for this: market share.

We could tax each corporation’s profits in direct proportion—or even literally equal to—its market share in a suitably defined market. It shouldn’t be too broad (“electronics” would miss Apple’s dominance in smartphones and laptops specifically) or too narrow (“restaurants on Broadway Ave.” would greatly overestimate the market share of many small businesses); this could pose some practical difficulties, but I think it can be done.


And what if a corporation produces in many industries? I offer a bold proposal: Use the maximum. If a corporation controls 10% of one market, 20% of another, and 60% of another, tax all of their profits at the rate of 60%.

If they want to avoid that outcome, well, I guess they’ll have to spin off their different products into different corporations that can account their profits separately. Behold: Self-enforcing antitrust.

Of course, we need to make sure that when corporations split, they actually split—it can’t just be the same CEO and board for 40 “different corporations” that all coordinate all their actions and produce subtle variations on the same product. At that point the correct response is for the FTC to sue them all for illegal collusion.

This would also disincentivize mergers and acquisitions—the growth of which is a major reason why we got into this mess of concentrated oligopolies in the first place.

This policy could be extremely popular, because it directly and explicitly targets big business. Small businesses—even those few that actually are C corporations—would see their taxes dramatically reduced, while trillion-dollar multinationals would suddenly find that they can no longer weasel out of the taxes every other company is paying.

Indeed, if we somehow managed to achieve a perfectly-competitive market where no firm had any significant market share, this corporate tax would effectively disappear. So any time some libertarian tries to argue that corporate taxes are interfering with perfect free market competition, we could point out that this is literally impossible—if we had perfect competition, this corporate tax wouldn’t do anything.

In fact, the total tax revenue would be proportional to the Herfindahl–Hirschman Index, a commonly-used measure of market concentration in oligopoly markets. A monopoly would pay 100% tax, so no one would ever want to be a monopoly; they’d immediately split into two firms so that they could pay a tax rate of 50%. And depending on other characteristics of the market, they might want to split even further than that.

I’ll spare you the algebra, but total profits in a Cournot equilibrium [PDF] with n firms are proportional to n/(n+1)^2, but with a tax rate of 1/n, this makes the after-tax profits proportional to (n-1)/(n+1)^2; this is actually maximized at n = 3. So in this (admittedly oversimplified) case, they’d actually prefer to split into 3 firms. And the difference between a monopoly and a trinopoly is quite significant.

Like any tax, this would create some incentive to produce less; but this could be less than the incentive against expanding monopoly power. A Cournot economy with 3 firms, even with this tax, would produce 50% more and sell at a lower price than a monopoly in the same market.

And once a market is highly competitive, the tax would essentially feel like a constant to each firm; if you are only 1% of the market, even doubling your production to make yourself 2% of the market would only increase your tax rate by 1 percentage point.

Indeed, if we really want to crack down on corporate tax avoidance, we could even charge this tax on sales rather than profits. You can’t avoid that by offshoring production; as long as you’re selling products in the US, you’ll be paying taxes in the US. Firms in a highly-competitive industry would still only pay a percentage point or two of tax, which is totally within a reasonable profit margin. The only firms that would find themselves suddenly unable to pay would be the huge multinationals that control double-digit percentages of the market. They wouldn’t just have an incentive to break up; they’d have no choice but to do so in order to survive.

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