Wealth Tax Smackdown: Zucman vs. Aghion Sparks Fireworks at FDday

September in Paris means two things: la rentrée and FDday, the French Tech ecosystem’s own back-to-school bash.

Once again under improbable blue skies, the Musée des Arts Forains filled up with founders, investors, operators and policy wonks, a buzzing crowd swapping stories of entrepreneurial success and strife with “great-to-see-you-again” hugs all around.

The mood for the most part was warm, inclusive, and upbeat. Which is more than can be said for France’s actual political scene, where shouting matches are the daily special. This year, FDday closed with a full-blown showdown over the “taxe Zucman.”

This shouting match featured a touch more intellectual glamour because it featured the man himself. Yes, that Zucman.

What the “Zucman" is this tax?

Gabriel Zucman, the French economist who has made a career studying wealth inequality, was commissioned last year by Brazil’s G20 presidency to sketch out how to make billionaires actually pay taxes. Yes, a shocking concept.

His report, "Blueprint for a Coordinated Minimum Effective Taxation Standard for Ultra-High-Net-Worth Individuals" dropped in June 2024.

The idea is a global 2% minimum tax on the wealth of billionaires with assets amounting to over $100 million. Countries can tweak thresholds and mechanics as they see fit. The point is to close the loopholes that let the very richest pay tax rates that are proportionally lower than those of the middle and working classes. 

France’s Green party seized on it.

In February 2025, MP Éva Sas tabled a bill creating a 2% minimum wealth tax for fortunes above €100 million, including business assets. Team Zucman estimated that such a tax could bring as much €20 billion to state coffers. 

The French National Assembly passed it, the Senate promptly binned it in June, citing difficult calculation methods, constitutional weaknesses, valuation headaches, liquidity traps for founders and, horror of horrors, the risk of clipping France’s AI unicorns mid-flight forcing them to flee la France.

Meanwhile, France continues to flounder politically and economically.

Earlier this month, Prime Minister François Bayrou lost a vote of no confidence in a landslide. He had called the vote in hopes of resolving the deadlock over his plans for a severe austerity budget (including plans to cut two banking holidays) to address the nation's yawning budget deficit.

President Emmanuel Macron appointed Sébastien Lecornu as the new Prime Minister. Fitch Ratings downgraded the nation's credit ratings. It remains unclear how Lecornu plans to close the budget gap.

Of course, this need for cash re-opened the door for the 2% wealth tax.

Zucman, a professor at the prestigious Ecole normale supérieure and director of the Observatoire européen de la fiscalité, began advocating for it and left-leaning parties are calling for Lecornu to include a 2% tax on households with assets above €100 million.

A recent IFOP poll shows 86% of the French public in favor.

Let’s just say the vibe among founders is less enthusiastic. This is a particularly sensitive topic among French techies for a couple of reasons.

The first is historic. La French Tech was founded on a tax revolt more than a decade ago. When President François Hollande proposed a massive capital gains tax, a coalition of investors and entrepreneurs organized a movement they dubbed Les Pigeons (the suckers). Not only did they persuade Hollande to change his mind on the tax, but he made a total political shift and oversaw the creation of La French Tech Mission and replaced his lefty Economic Minister with an unknown upstart named Emmanuel Macron.

Second: For founders such as the newly minted billionaires of Mistral AI, the wealth exists on paper. So the notion of how it is actually valued is somewhat vague.

The Big Debate: Aghion vs. Zucman

Enter FDday’s closing act: a head-to-head between Gabriel Zucman himself and Philippe Aghion, the former Harvard University economist and now professor at the Collège de France, and darling of the innovation crowd.

The atmosphere crackled. It was serious economics but with the energy of a prize fight.

Here's a recap of their key points:

Aghion’s case (a.k.a. “Don’t strangle the unicorns”):

• “I’m talking about entrepreneurs whose wealth is not realized, who aren’t cashing out millions but are reinvesting everything back into their companies.”
• “We mustn’t bridle innovation or force founders to sell their companies to foreign buyers. Otherwise, we miss the AI revolution.”
• “Is it fair to tax a volatile, unrealized valuation as if it were cash in the bank?”

Then, with a mischievous flourish, he threw out a menu of “why nots?”:

• A smaller Zucman, say 0.5% with exemptions for younger firms.

• A differential contribution excluding working assets.

• Taxing idle wealth in family holdings.

• Even a return of the L'impôt de solidarité sur la fortune, a kind of minimum wealth tax.

All ways, he argued, to chase fairness without kneecapping founders.

Zucman’s rebuttal (a.k.a. “It’s only 2%! Relax!”):

• “We’re talking about 1,800 households with over €100 million. If you already pay enough tax, you owe nothing more. This is just a floor.”
• “The cashier pays more in VAT at the checkout than some billionaires do in effective tax rates. That’s not justice.”
• “The Mistral AI cases? A few dozen exceptions. Important, yes, but not the rule. We’ll figure out solutions. But let’s not blow up the reform for a handful of edge cases.”

It was sharp, impassioned, occasionally barbed. The crowd, many of them founders in precisely that “volatile valuation, zero liquidity” situation, leaned toward Aghion.

But Zucman held his ground with the moral clarity of a man convinced that billionaires should not pay less tax than the middle and working classes.

Where does that leave us?

Both economists want fairness. Both know innovation matters. The fight is over the “how,” not the “whether.”

As Aghion put it: “We’re already one of the most heavily taxed countries in the world. Let’s tweak, not torch.”

As Zucman countered: “It’s just a minimum floor. Two percent. Fairness is non-negotiable.”

If the goal was to end a great FDday with fireworks and food for thought, then the Mission was accomplished!