A study by the University of Manchester has found that human sperm quality peaks in June and July, peaking out in December and January. The study involved analyzing semen samples from over 15,500 men aged 18 and 45 who applied to be sperm donors between 2018 and 2024. The researchers found that "progressive motility" was significantly improved across both populations. However, the study's co-author, Allan Pacey, suggested that potential sperm donors might have better odds of acceptance if they applied in warmer months. The findings also revealed that sperm motility was highest in men in their 30s and declined in men under 25 and over 40.