A plan to use family planning and other tools to help families save money has been gaining momentum since it was unveiled in a federal health care law passed last year.
But the California Family Planning Commission said in a study released this month that only 13 percent of couples are using it.
The findings were based on surveys of 1,000 women, aged 20 to 49, who answered questions about their household income and household use of contraception.
The data was collected between October and December and included questions about contraception and family planning use.
The commission did not say whether the survey was intended to gauge how much people would use family and contraception.
Agency officials said the commission is still working on a methodology for analyzing the data and that a final report would be released in late spring or early summer.
“We know that most women are using contraception, so this is really a very small percentage,” said Dr. John Wahlstrom, a family health physician and vice president of research and development at Kaiser Permanente, which is helping fund the research.
“But the fact that only about 13 percent are using family and that most of them have access to it makes it a very promising area.”
The study, conducted by the Center for Family and Community Health at the University of California, San Francisco, looked at the percentage of women who reported they had used a contraceptive method at least once in the previous month and whether they were using it regularly or not.
In California, the percentage who used a birth control method at some point in the past 12 months was about 60 percent, and the percentage using it more than once in a month was about 40 percent.
The study found that in 2014, more than 1.2 million women were using a contraceptive at some time in the month, about 815,000 of them who were pregnant.
About 2.7 million of them were using the method at more than one time, about 1.7 percent of the population.
The percentage of those using the birth control at least one time fell to about 5 percent in 2015.
The rate for the past two years was less than 1 percent, according to the report.