The increasing rate of fertility is a big problem in developing countries. In Pakistan, this trend is quite different in provinces. The objective of this study is to identify the social, economic, and demographic determinants of fertility in Pakistan and how underweight and obesity effects it. In this study fertility rate of women in Pakistan has been measured through the total number of children ever born per woman. Data has been collected from the Demographic Health Survey of Pakistan and segregated into Punjab, Sindh, Baluchistan, FATA, and KPK. Women’s Body Mass index is used to find out the prevalence of underweight and obesity. The results showed that socioeconomic determinants of women’s fertility have been showing different effects on fertility in different provinces of Pakistan. Women’s education harms women’s fertility in Pakistan. A negative effect of husbands’ education on women’s fertility has been revealed in Pakistan. In Pakistan, women’s fertility has increased by not using contraceptives in Sindh and Balochistan. Husband’s age has also been proven to have a positive effect on women’s fertility in KPK and Punjab. The husband’s desire not to have more children harms women’s lives in Punjab as compared to other provinces. Women’s employment before marriage has also been found to have a positive relationship with women’s fertility in Punjab, Sindh, and Balochistan. At the same time, being underweight have negative and obese have a positive impact on fertility in all provinces of Pakistan.