Fertility factors are determinants of the number of children that an individual is likely to have. Fertility factors are mostly positive or negative correlations without certain causations.
Factors generally associated with increased fertility include the intention to have children, in advanced societies very high gender equality, religiosity, inter-generational transmission of values, marriage and cohabitation, maternal and social support, rural residence, pro family government programs, low IQ and increased food production.
Factors generally associated with decreased fertility include rising income, value and attitude changes, education, female labor participation, population control, age, contraception, partner reluctance to having children, very low level of gender equality, infertility, pollution, and obesity.
The predictive power of intentions continues to be debated. Research that argues that intentions are a good predictor of actual results tends to draw ideas from the theory of planned behavior (TPB). According to the TPB, intentions stem from three factors: attitudes regarding children, including the cost of raising them versus perceived benefits; subjective norms, for example the influence of others; and perceived control over behavior, that is, how much control an individual has over their own behavior.
Fertility intentions tend to boil down to quantum intentions, or how many children to bear, and tempo intentions, meaning when to have them. Of these, quantum intention is the poor predictor because it tends to change as a result of the ups and downs of a typical life. Tempo intention is a somewhat better predictor, but still a weak way to predict actual results.
The intention to have children generally increases the probability of having children. This relation is well evidenced in advanced societies, where birth control is the default option.
A comparison of a survey to birth registers in Norway found that parents were more likely to realize their fertility intentions than childless respondents.