The Supreme Court ruled that some employers with religious objections don't have to cover birth control in their health plans.
But more than half of privately insured women are already getting free birth control under President Barack Obama's health law. That's a major coverage shift—and likely to advance.
Recent data from the IMS Institute document what was a sharp change during 2013.
The share of privately insured women who got their birth control pills without a copayment jumped to 56 percent, from 14 percent in 2012.
The law's requirement that most health plans cover birth control as prevention, at no additional cost to women, took full effect in 2013.
The average annual saving for women was $269.
Explore further: Insurers must cover birth control with no copays