[User23]

It's not a flat percentage exactly and it varies by state[1]. I'm not sure how I got 10% in my head maybe that's roughly the average?

[1] https://calmatters.org/projects/california-keeps-millions-in...

[giantg2]

That article says the average retained is about 3.8% nationally. It sounds like what the government is getting it from interest on unpaid support.