According to the Medical Expenditure Panel Survey—Insurance Component 2018 Chartbook, among private-sector establishments offering health insurance in 2018, enrolled employees paid 21.3% of the premium for single coverage, 27.1% for employee-plus-one coverage, and 27.8% for family coverage.
Survey results can be obtained at https://meps.ahrq.gov/data_files/publications/cb23/cb23.shtml.