It’s High Time for Conception: Studies Show Peak Times, Weather for Sex

It's peak season for baby making. Anneli Rufus on the days when you stand the best chance of having sex.

Philip Harvey / Corbis

Studies show that the most common birthday—the one shared by the largest number of people nationwide—is September 16. This means most babies are conceived during the winter holiday season—hey, that’s right around now. When else do couples get lucky? At midnight, during spring break, when it rains, and when they haven’t just lost their jobs, recent research reveals.

1. Conception rates reach their annual peak in December, with 9 percent of all U.S. conceptions occurring during that month.

August is the annual “trough,” with the year’s fewest number of conceptions. The University of Texas–affiliated study that yielded this stat confirms similar findings in many other studies showing that most babies are born in late September, while the fewest are born in April. “Biologic hypotheses include deterioration of sperm quality during summer, seasonal differences in anterior pituitary-ovarian function caused by changes in the daylight length, and variation in quality of the ovum or endometrial receptivity,” the study’s authors write. “Increased sexual activity associated with end-of-year holiday festivities has also been postulated.”

Alan Tita, et al. “Seasonality in Conception of Births and Influence on Late Initiation of Prenatal Care.” Obstetrics & Gynecology, 97 (6): 976-981.

2. More than twice as many condoms are sold in the week before Christmas than in the week after Christmas.

This sales pattern is “strongly suggestive of an acute increase in sexual activity over the Christmas period,” write the authors of the scholarly study that yielded this stat. “The sharp increase in sales in the week before Christmas and the sharp fall in sales in the week after Christmas indicate some stockpiling.” The rise in sexual activity during late December “has been interpreted largely in the context of merrymaking. The period from Christmas to the New Year is associated with increased opportunities for socializing and a generally more hedonistic approach to life,” the authors write.

K. Wellings, et al. “Seasonal Variations in Sexual Activity and Their Implications for Sexual Health Promotion.” (PDF) Journal of the Royal Society of Medicine, 92 (2): 60-64.

3. People are 17 times more likely to have sex at midnight than at 10 a.m.

A study published in the Journal of Circadian Rhythms sought to determine the times of day at which its participants had sex over a three-week span. The vast majority had sex at bedtime, which ranged from 11 p.m. to 1 a.m. “People have sex subject to availability, and when they are partnered, bedtime not only provides that availability, but it possesses a certain amount of cultural coding,” says sexologist Carol Queen, author of Exhibitionism for the Shy: Show Off, Dress Up and Talk Hot. “That is, there’s an expectation that this is an acceptable, desirable or ‘normal’ time to have sex. Besides, many people find sex has a relaxing and even sleep-inducing quality, which makes it a logical end-of-day activity.”

Roberto Refinetti. “Time for Sex: Nycthemeral Distribution of Human Sexual Behavior.Journal of Circadian Rhythms, 3 (1): 4.

4. When the tax benefits of having a child are increased by $500, the probability of that child being conceived so as to be born during the last week of December rises by 27 percent.

Does the idea of a refund make you hot? “Because the annual tax savings associated with a birth are realized if the birth takes place any time before midnight January 1, parents... have an incentive to time the birth at the end of December rather than at the beginning of January,” write the authors of the Syracuse University–affiliated study that yielded this stat.

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Stacy Dickert-Conlin and Amitabh Chandra. “Taxes and the Timing of Births.” (PDF) Journal of Political Economy, 107 (1): 161-177.

5. While most babies born in the U.S. are born in late September, with nearly 2 percent more being born then than in early April, the September-April gap widens to 3 percent in Alabama.

“The annual spring decline in births may be attributed to interrelated factors, but primarily to the discomforts of high summer temperatures and high humidity. This discomfort...probably reduces the frequency of coition and consequently of conceptions,” wrote the authors of the Ohio State University–affiliated study that yielded this stat. The study was conducted in 1959, before air-conditioning became ubiquitous. The September-April gap slims to 1 percent in states with less sultry summers, such as Washington and Maine.

Benjamin Pasamanick, et al. “Geographic and Seasonal Variation in Births.” (PDF) Public Health Reports, (74) 4: 285-288.

6. People are 13 times more likely to have sex at night than in the afternoon.

Participants in the study that yielded this stat reported that the timing of their sexual encounters was more about convenience than degree of sexual desire. “They cite family, work schedules, etc., which result in the postponement of sex,” Queen notes. “And look how few were having sex in the afternoon! Tragic. This interests me as a sexologist because there’s some indication that tiredness can lower the quality of sex, possibly upping the degree of dissatisfaction one or both partners might have about their sex life. Waiting until just before bed certainly has its logic and is the time when sex may be most easily negotiated, but I hope readers will ask themselves whether their sex lives are being experienced at the optimal times” to suit their own needs.

Roberto Refinetti. “Time for Sex: Nycthemeral Distribution of Human Sexual Behavior.Journal of Circadian Rhythms, 3 (1): 4.

7. Sunday is the least popular day for sex; Friday and Saturday are 18 percent more popular.

At least, that’s how it was for the teenagers afflicted with sexually transmitted disease whose “coital events” were the subject of the University of Indiana–affiliated study that yielded this stat. “The proportion of coital events associated with drugs or alcohol increased from Sunday to Saturday,” its authors write. In contrast with national norms, for this demographic “intercourse was most common in spring and summer, and least frequent in winter.”

JD Fortenberry, et al. “Weekly and Seasonal Variation in Sexual Behaviors Among Adolescent Women With Sexually Transmitted Diseases.Journal of Adolescent Health, 20 (6): 420-425.

8. Men who have sex with men have 10 percent more sex on Sundays than on Tuesdays.

According to a 2010 Thai Ministry of Public Health/U.S. Centers for Disease Control and Prevention–affiliated study that surveyed men in Bangkok who had sex with other men, 27 percent of those who had had sex in the week before being surveyed had had it on Monday; 23 percent had had it on Tuesday, Wednesday or Thursday; 28 percent had had it on Friday, 32.6 percent on Saturday, and 33.1 percent on Sunday.

Frits van Griensven, et al. “Sex Frequency and Sex Planning Among Men Who Have Sex With Men in Bangkok, Thailand: Implications for Pre- and Post-Exposure Prophylaxis Against HIV Infection.Journal of the International AIDS Society, 13 (1): 13.

9. Fifteen to 17 percent of adolescent intercourse occurs between 3 p.m. and 6 p.m.

But most of it happens at night, according to the University of Indiana–affiliated study that yielded this stat. Teen sex is “more than twice as likely to occur after 6 p.m. than in the afternoon,” the authors write. Increasing the chances of afternoon sex are “an argument with a partner, partner emotional support, time spent with a partner”—and skipping school.

JD Fortenberry, et al. “Weekly and Seasonal Variation in Sexual Behaviors Among Adolescent Women With Sexually Transmitted Diseases.Journal of Adolescent Health, 20 (6): 420-425.

10. Nearly twice as many people have turned down offers of sex because the temperature was too high than have turned down offers of sex because the temperature was too low.

In the Degrees of Pleasure study conducted for the Trojan condom company, 35 percent of participants said that they had refused to have sex at least once in their lives “because I was too hot,” while only 19 percent of participants said that they had refused to have sex at least once in their lives “because I was too cold.” It’s amazing what a few blankets can do.

Trojan’s Degrees of Pleasure Study (2010) (PDF)

11. Eleven percent of women and 55 percent of men expect to have sex during spring break.

And 25 percent of women and 28 percent of men actually do have spring-break sex, according to a Canadian study published in the Journal of Sex Research. The study also examined the sexual behavior of Australian students during what is known Down Under as “schoolies”: the week in late November–early December after high-school seniors complete their final exams. “Two-thirds of males and one-third of females expected to have sexual intercourse during their schoolies,” reads the report. “About 40 percent experienced sexual intercourse, with 61.4 of these reporting that they had sex with a casual partner.”

Eleanor Maticka-Tyndale, et al. “Casual Sex Among Australian Schoolies.Journal of Sex Research, 40 (2): 158-169.

12. Men and women facing job insecurity are 53 and 47 percent more likely, respectively, to experience low sexual desire than men and women not facing job insecurity.

No paychecks? No sex. Unemployment or even the fear of unemployment significantly lowers libido, according to a study affiliated with Switzerland’s University of Lugano, which examined the effects of job insecurity on men and women aged 20 to 49 and yielded this stat. “Although preliminary, this analysis also provides indications that stressful events such as restructuring, downsizing, privatization, mergers, and closures could also affect the family or intimate relationship life of workers,” reads the report.

Gianfranco Domenighetti, et al. “Impact of Job Security on Sexual Desire: An Exploratory Analysis.” (PDF) Swiss Medicine Weekly, 139 (33-34): 486-492.

13. Eighty-three percent of Americans rate rainy days and nights as the best time to have sex.

Well, yeah—because what else is there to do when you can’t play golf or drive with the top down? In Trojan's Degrees of Pleasure study, which surveyed adults nationwide, participants pegged the perfect temperature for sex at between 68 and 70 degrees. “Mother Nature really can bring people together,” Queen says.

Trojan’s Degrees of Pleasure Study (2010) (PDF)

14. Ten percent more 2005 Mardi Gras attendees had oral sex with strangers they met during the festivities than had anal sex with strangers they met during the festivities.

The study that yielded this stat examined sexual activity during New Orleans’s 2005 Mardi Gras festivities. Thirty-two percent of its subjects reported engaging in vaginal sex, 16 percent in oral sex and 6 percent in anal sex—in all cases, with people they met at Mardi Gras. The study also examined Mardi Gras attendees’ expectations: Twelve percent of women and 45 percent of men “reported intending to have vaginal sex with someone they met at Mardi Gras,” while 19 percent of men and 5 percent of women “reported expecting to engage in anal sex.” “It’s easier to have oral sex than either kind of intercourse, in terms of preparation, location, etc.—particularly fellatio,” Queen says. “Many people think of oral sex as a kind of ‘sex lite’; it’s an easier decision to decide to do it, certainly compared to anal sex. Anal, in particular, generally requires more skill and negotiation—at least to do it right.”

Robin Milhausen et al. “A Theory-Based Approach to Understanding Sexual Behavior at Mardi Gras.Journal of Sex Research, 43 (2): 97-106.

15. The likelihood of scoring a successful pickup is considered 56 times better on Friday than on Monday.

At least, that’s true in Tokyo. And that’s according to readers of Time Out Tokyo, whose 2011 Sex Survey probed for data on when and where Tokyoites do it, how often, and with whom. Asked which day of the week is the most likely on which to get lucky, 56 percent of readers picked Friday, 30 percent Saturday, 6 percent Thursday, 3 percent Wednesday; 3 percent Sunday; 1 percent Tuesday, and another 1 percent Monday.

Time Out Tokyo, The Sex Issue: Tokyo Sex Survey, 2011