Context Profitability of water buffalo systems depends on a calving interval (CI) >400 days. Several factors affect the achievement of this target. However, milk yield at first lactation has received little attention. Aims Determine the effect of milk yield at first lactation, parity, season of calving and farm, on the length of CI and the probability of a CI 400 days in water buffaloes. Methods A retrospective analysis of milk yield at first lactation and reproductive records of 1459 water buffaloes was carried out. Milk yield was categorised as Group 1 (1090 kg), Group 2 (10901377 kg), Group 3 (13771684 kg) and Group 4 (<1684 kg); parity was categorised as parity 1, 2 and 3; and month of calving was grouped into three seasons: DecemberMarch, AprilJuly, and AugustNovember. Data were analysed using linear and logistic mixed models. Key results CI increased from 425.3 days (95% CI: 418.8431.8 days) in group 1 to 463.3 days (95% CI: 456470.6 days) in group 4 (P > 0.05), while the probability of having a CI 400 days decreased from 0.5 (95% CI: 0.460.54) to 0.26 (95% CI: 0.220.29), respectively (P > 0.05). CI decreased from 466 days (95% CI: 460.8471.3 days) in parity 1 to 410.5 days (95% CI: 405.2415.8 days) in parity 3, whereas the probability of a CI 400 days increased from 0.26 (95% CI: 0.240.29) to 0.51 (95% CI: 0.470.54) respectively (P > 0.05). Water buffaloes calving in AugustNovember showed significantly shorter CI and, along with those calving between DecemberMarch, showed the highest probability of a CI 400 days. An interaction between milk yield at first lactation and parity on both outcomes was observed. Conclusions Shorter CI and higher probability of a CI >400 days were associated with lower milk yields at first lactation, higher parity and calving between AugustNovember. Higher milk yield at first lactation affected negatively the reproductive performance of water buffaloes, especially at parity 1 and 2. Implications These results highlight the importance of adequate nutritional management to allow water buffaloes to cope with the challenge of the postpartum negative energy balance and have a calving interval less than 400 days.