Michaël Zemmour

France's 10-year borrowing rate has been flirting with 5%.

Yet BNP Paribas senior economist Stefan Koliak puts France's effective interest rate – the average it actually pays across all its debt – at just over 2%.

That's about the same as the Netherlands.

How can both be true? The answer is that a national debt isn't one loan.

At 91 billion euros a year, France pays roughly 2,900 euros in interest every second.

And none of that money builds a school, a hospital or a tank.

Now for the arithmetic economists actually use.

It's called the snowball effect and it's simpler than it sounds.