IntroductionThe timely initiation of complementary feeding is essential to reduce infant mortality. In Ethiopia, 37.5 % of mothers did not initiate complementary feeding to their infants in time. However, previous studies could not identify the time to initiate complementary feeding among primipara mothers. Therefore, this study aims to identify the time to initiate complementary feeding and its predictors among primipara mothers with infants aged 6–12 months in the Awi zone, northwest Ethiopia. MethodsA community-based retrospective follow-up study was conducted among 732 primipara mothers who had infants aged 6–12 months from January 1, 2022, to December 30, 2022. A multistage sampling technique was used to select study participants through questionnaires administered by interviewers. Data were entered into EPI-data 3.1 and exported to STATA 17 for further analysis. The Kaplan-Meier survival curve together with the log-rank test was used to assess the survival experience of the infant at specific times and to compare the survival of the infant in it between different categorical independent variables. Bivariable and multivariable Cox proportional hazard regression models were used to identify significant predictors. Model fitness was also assessed using the Schoenfield residual and the Cox-Snell global residual test. Statistical significance was declared at the p-value <0.05. ResultThe median time to initiate complementary feeding among primipara mother-infant pairs was 6 ± 2 months. The overall incidence rate of complementary feeding initiation before, at and after 6 months of age of the infant was 7.28 (95%CI: 6.44, 8.25), 41.41 (95%CI: 36.05, 47.56), and 42.97 (95%CI: 36.89, 50.05) per 100 person-month observations, respectively. Among those mothers who initiated complementary feeding for their infants, 249, 200, and 165 initiated complementary feeding before, at and after 6 months of age of the infants. Furthermore, the age (15–24 years) of mothers (AHR: 1.63, 95%CI: 1.16, 2.29), rich wealth (AHR: 1.35, 95%CI: 1.05, 1.75), and richest wealth (AHR: 1.43, 95%CI: 1.10, 1.84) were identified as statistically significant predictors of the time to initiate complementary feeding. ConclusionsThe median time to initiate complementary feeding among primipara mother-infant pairs was 6 months. The age of the mother and the wealth status of the household were found to be statistically independent predictors of the time to initiate complementary feeding. Therefore, community health professionals are better able to work on when to initiate complementary feeding to infants of rich and richest young primipara mothers.