We investigate the impact of the Affordable Care Act's dependent coverage mandate on insurance premiums. The expansion of dependent coverage under the ACA allows young adults to remain on their parent's private health insurance plans until the age of 26. We find that the mandate has led to a 2.5–2.8 percent increase in premiums for health insurance plans that cover children, relative to single-coverage plans. We are able to conclude that employers did not pass on the entire premium increase to employees through higher required plan contributions.