People are having less sex because of the distractions of modern day life, including smartphones and social media websites, researchers said.
A survey of over 15,000 Britons showed that those between 16 to 44 were having sex fewer than five times a month, the National Survey of Sexual Attitudes and Lifestyles (Natsal) found.
That figure was down from previous surveys in 1990-91 and 1999-2001 when couples were having sex more than six times a month.
University College London's Dr Cath Mercer said money and job worries meant people were "not in the mood for sex".
She added: "We also think modern technologies are behind the trend too. People have tablets and smartphones and they are taking them into the bedroom, using Twitter and Facebook, answering emails."