Less than half of custodial parents in the US recieve full child support due
https://www.census.gov/newsroom/press-releases/2018/cb18-tps03.html
- About half (50.2 percent) of all 13.6 million custodial parents had either legal or informal child support agreements. Custodial mothers were more likely to have agreements (52.7 percent) than custodial fathers (39.6 percent).
- The aggregate amount of child support due in 2015 was $33.7 billion, a decrease of $14.0 billion from 2003.
- About 60 percent of the child support due in 2015 was reported as received, averaging $3,447 per year per custodial parent who was due support.
https://www.census.gov/library/publications/2018/demo/p60-262.html
Child support is calculated (in the states at least)as a percentage of the non custodial parents income. This can be varying or flat.
The situation with parents not paying is not much better in Ireland. And for a while some parents got away with not paying child support after the age of
seven. https://www.thejournal.ie/child-maintenance-3750905-Dec2017/Arrears in maintenanceare common.
Though they are getting though.
https://www.breakingnews.ie/ireland/10-days-jail-for-dad-accused-of-not-paying-enough-maintenance-826118.html Last year this judge sent a father to jail for 10 days for failing to pay child maintenance.