Sex and happiness go together like a horse and carriage. But how often do you need to ride to be the happiest together? For most couples, the answer is…

A. Less than once a month

B. About once a month

C. About once a week

D. 2 or 3 times a week

E. 4 or more times a week

The correct answer is—C. About once a week.

That fact comes from a new study that has several surprising insights about sex and happiness—for both men and women, in relationships or single, at any age. Read on to learn more.

UPENDING THE SEX CHALLENGE MYTH

For couples in a long-term relationship, married or not, sex on a weekly basis is linked to optimal happiness and satisfaction with the relationship, found researchers at University of Toronto Mississauga, who analyzed surveys of 30,000 men and women taken over several years.

Those who had sex two, three, four or more times a week weren’t less happy—but they weren’t happier either.

The results run counter to the “daily sex challenge” fad that’s been going on for a while now and is all over the Internet, where couples are supposed to improve their relationships by having sex every day for a month or even longer. But the results didn’t surprise Amy Muise, PhD, a postdoctoral candidate at University of Toronto and one of the study authors. She pointed to an earlier study that asked couples that were already having sex about once a week to double that frequency, and compared them to another set of couples who stayed with the same frequency. Result: No increase in well-being. The new study adds a few twists…

• For couples, the difference between having sex less than once a month compared with once a week was a big increase in happiness. How big? The happiness difference was comparable to that seen when going from poverty or near poverty (income of $15,000 to $25,000 a year) to a middle-class income ($50,000 to $75,000 a year).

• The primary way that weekly sex drives happiness in couples, the researchers found, is that it is associated with more satisfaction with the relationship. While sex itself is pleasurable, of course, its main contribution to happiness seems to be that it makes you feel better about your partner and your relationship for days afterward.

• For people not in established relationships as couples, there was no link between sexual frequency and happiness. For them, having more frequent sex was not associated with more—or less—happiness.

• Once-a-week sex was the sweet spot for both men and women. Men may report higher desire than women, says Dr. Muise, but there was no difference between genders in sexual frequency and happiness.

• The weekly “golden mean” seems to apply across ages, too. “We do find that couples engage in sex less frequently over time,” says Dr. Muise. “That’s related to both age and relationship duration. But our results suggest that the pattern, where sex is no longer associated with greater happiness after about once a week, is consistent across ages.”

The bottom line? Of course, any particular couple should have sex exactly as often as that couple wants to have sex. But we all know that both partners don’t always agree on what that number should be…and even when they do agree, sometimes life gets in the way of following through. So for those couples, instead of focusing on a “more would be better” approach—which can only be frustrating over time—the best advice for happiness is “just enough,” meaning once a week. For most couples, that’s the happy medium.