What you (probably) didn’t know about the math behind the Dutch electoral system

On October 29, Dutch citizens will head to the polls once again. What few people realise is that there’s a surprising amount of mathematics at the core of our democracy. What calculations determine who ends up in parliament? Flemish mathematician Filip Moons, assistant professor Mathematics Education at the Freudenthal Institute, dug into the numbers behind the Dutch electoral system and even wrote a book about it: From Vote to Seat (Van Stem tot Zetel).

“What’s quite interesting,” Moons points out, “is that in the Netherlands, the place where you cast your vote makes no difference to the outcome. Whether you vote in Groningen or Rotterdam, every vote carries exactly the same weight. In almost every other country, including Belgium, there are electoral districts that determine how many representatives each region gets. You only vote for the seats assigned to your district.” Only Serbia, Slovakia, and Israel fill their parliaments the same way the Netherlands does.

If we used electoral districts in the Netherlands, half of the current parties would probably disappear.

World champion in fragmentation

The choice for one national constituency has consequences. “It’s the reason we see so many more parties in the Dutch parliament than in Belgium,” Moons explains. “If we used electoral districts, half of the current parties would probably disappear.”

That fragmentation is no accident. Over a century ago, the so-called Oppenheim Commission deliberately chose maximum proportionality: every vote had to count equally. “It was also meant to break through the old pillarised system,” Moons says. “Otherwise, the Catholic south would have ended up with a far larger share of seats than it actually deserved nationally. The side effect is that the political landscape became much more fluid and parties can emerge and vanish more easily.”

Belgian invention

It was a Belgian person, Victor D’Hondt, who laid the groundwork for the Dutch system. In 1892, the Ghent-based lawyer designed a method for allocating seats proportionally. That was something that had never been done before. “It’s hard to imagine now, but his idea was revolutionary,” says Moons. “Young democracies, including the Netherlands, mostly used district systems at the time: whoever won a district went to parliament, and all other votes were simply lost. D’Hondt’s system made it possible to use all votes to distribute seats proportionally.” The Netherlands adopted that principle, but took it even further by removing all regional corrections.

Stories behind the numbers

The book From Vote to Seat is far from a dry textbook, and Moons hardly uses any formulas. He explains the logic of the system through examples and short historical stories. This way, he hopes readers will rediscover the care with which the Dutch system was once designed. “It’s 120 years old, and hardly anything has changed. That tells you something about how well it works.”