In variety of ways, Demographers measure the rate of fertility. The total rate of fertility is number of children would bear by woman during her lifetime and if she were to experience prevailing specific-age fertility rate of women. In human fertility both men and women have some hormonal cycles that determine when both women can achieve the pregnancy and men are most virile. Female cycle is approx: 28 days long, while male cycle is variable.

A man can ejaculate as well as produce sperm any time of month, where quality of sperm dips occasionally.

Although a woman can pregnant at any time when her menstrual cycle is active, but peak fertility also occurs during some days of cycles. It occurs two days before or after ovulation date usually. In this fertile widow, it varies from one to another woman; ovulation dare varies from the cycle to cycle for same woman.

In female fertility average age of menarche in United States is near 12.5 years. Fertility of women peaks around 19 to 24 years of age and it decline after 30 years. In men, erectile dysfunction increase with age, while fertility does not decline in men as it does in women. Some examples have been there that males fertile at the age of 94 years, however these evidence has also suggest that increased age of male is associated with decline in sperm motility, semen volume and sperm morphology.