The weight of cows at calving is not a trait commonly measured by producers, but may influence milk yield and reproduction because of the negative energy balance. The effect of calving weight on milk yield of dairy Gyr cows was analyzed using data from 2 herds comprising 570 records of total yield during lactation of 363 cows that had calved between 2000 and 2014. The contemporary groups containing at least 5 observations were defined as herd and year and season of calving. The latter was divided into dry season (April to September) and rainy season (October to March). The analyses were performed using linear models containing the fixed effects of contemporary group and lactation duration (linear coefficient), and by regression of milk yield on calving weight nested within classes of age at calving (1 to 8), with class 1 corresponding to animals aged 2 to 3 years and so on until animals aged 10 years at calving. The PROC GLM module of the SAS program was used for analysis. The mean calving weight was 434.156 kg and this trait was influenced by age of cow at calving (linear and quadratic effects). The trend of regression indicated an increase in calving weight up to 90 mo, declining thereafter. The effect of calving weight for each class of age at calving presented linear regression coefficients of 5.19, 7.34, 9.33, 8.97, 2.43, −0.93, −3.70 and −4.97, respectively. These results demonstrate an increase in calving weight and total yield until physiological maturity, which occurs in this breed at about 93 mo when production starts to decrease slowly with increasing age of the animal. The influence of calving weight on milk yield is more important for younger cows. This importance decreases for older cows as expected, since they have stopped growing and have reached their maximum genetic production potential. Furthermore, older cows produce less milk compared with younger animals whose genetic potential for milk production and lactation persistence is higher due to the genetic improvement performed.