[usr1106]

The additional mandatory fees are around 30% https://sv.m.wikipedia.org/wiki/Arbetsgivaravgifter_i_Sverig...

So with 4 kEUR gross salary you end up at 5.2 kEUR cash costs. Then there are also non-cash costs, like 5 weeks of paid holidays (or did unions actually achieve the 6th one? It's 30 years I lived in Sweden...)

And you might need an office, equipment, and what not. So the cost can easily be 6-7 kEUR even if the developer sees only 4 kEUR on their payslip.

A few might earn (significantly) more. But that's more likely in corporations higher levels than for open source related development work.

[mongol]

Yes. An employer must also take into account the average sick time per employee and year, since it pays for sick pay day 2 - 14 when the employee is sick. That is an another contribution to the 2x ballpark number.

[usr1106]

In Germany you pay/get 13 - 14 monthly salaries per year. In Finland 12.65. Don't know the figure for Sweden, but I'm pretty sure it's > 12.