Sundays really are Fundays.

Research shows that weekends are the prime time for between the sheets action, particularly Sunday. An analysis of Instacart data, which offers grocery and other delivery from local stores, from this week shows that Sunday is a very popular day for buying condoms. And a British study of 2,000 people released earlier this year found that Sunday morning was the most popular time during the week to get frisky, followed by Saturday.

Whether you’re doing it on the weekends or during the week, however, may have to do with whether you’re in a relationship or not. Single women were most likely to have sex from Monday – Thursday, while women in relationships were doing it on the weekend more, according to a study published in 2014 in The Journal of Sexual Medicine.

But no matter how you slice the data, a lot of people aren’t having sex during the week much, if at all. And that’s a problem for employers. The reason: Sex makes you a more productive worker, according to a study published in March in the Journal of Management.

The study authors found that “when employees engaged in sex at home, they reported increased positive affect at work the following day” and that “sex at home increased both daily job satisfaction and daily job engagement.”

So how do you make time for a little lovin’ during the week? Experts suggest that you put sex on your to-do list, make regular date nights and go to bed early (and naked). And try to have sex at least once a week, which is associated with a higher level of happiness, according to a 2015 study published in the journal Social Psychological and Personality Science.