If it seems your sex life isn't what it once was, you're not alone.

A new study suggests fewer people in the U.S. are living with partners and those who are married or living together are having less sex.

The study "Declines in Sexual Frequency among American Adults, 1989–2014" was published in the Archives of Sexual Behavior.

One reason Americans may be having less sex is that they are unattached, with just 59 per cent of people living with a partner in 2014, compared with 66 per cent in 1986, the study said.

Researchers from San Diego University in California, Widener University in Chester, Penn., and Florida Atlantic University in Boca Raton, Fla., used data from the U.S. General Social Survey which posed questions to a representative sample of 26,620 American adults from 1989-2014.

They found the biggest decline was in sexual frequency in couples who were in stable relationships.

In 1990, married couples typically had sex 73 times a year, but by 2014, they had sex 55 times a year, according to researchers from San Diego University in California, Widener University in Chester, Penn., and Florida Atlantic University in Boca Raton, Fla.

Singles now have more sex than couples

It used to be that singles had less sex overall than people in couples, but single people are reporting having sex 59 times a year, about the same as in 1990 and more than couples.

Jean Tenge, a San Diego State University psychology professor and co-author of the study, points out that sexual frequency declines with age and people are now getting married later in life.

They also have children later, so parenting takes up more of the evening hours that might have been devoted to intimacy.

But she notes that frequency of sex declined sharply for both married and unmarried people starting in 2008, when electronic devices began to take more of people's time.

Devices that distract us

Smartphones premiered in 2007 and Netflix and YouTube were becoming big about the same time, providing a multitude of entertainment options.

"Our entertainment is more entertaining, and more on-demand than it once was," Twenge said. "There are a lot more things to do at 10 p.m. at home than there used to be."

The study found the number of hours people worked did not seem to have an impact on sexual frequency, nor did education or race.

But age did.

Americans in their 20s had sex an average of about 80 times per year, but that declines to 60 times a year by age 45 and about 20 times per year for those in their 60s.