The chance of becoming a father decreases with age as sperm quality deteriorates over time, researchers have warned.
Experts at the Huntington Reproductive Medicine Centre in Brazil based their analysis on 570 cycles of IVF treatment.
By using donar eggs of only young, healthy women, researchers were able to isolate the impact of the mans age upon the chance of conceiving.
The results show that male fertility reduces from 60% at age 41 to 35% at age 45, and drops far more rapidly among older men.
The sperm of older men is more likely to appear abnormal, which is linked to fertility problems. Men whose sperm seemed normal had a 22% increased chance of becoming a father compared to those with less healthy looking sperm.
It was previously thought that only women needed to worry about their ticking biological clock, but experts have advised that would-be fathers should not leave having children too late.