ImportanceThe American Academy of Otolaryngology–Head and Neck Surgery Foundation has recommended yearly surgeon self-monitoring of posttonsillectomy bleeding rates. However, the predicted distribution of rates to guide this monitoring remain unexplored.ObjectiveTo use a national cohort of children to estimate the probability of bleeding after pediatric tonsillectomy to guide surgeons in self-monitoring of this event.Design, Settings, and ParticipantsThis retrospective cohort study used data from the Pediatric Health Information System for all pediatric (<18 years old) patients who underwent tonsillectomy with or without adenoidectomy in a children’s hospital in the US from January 1, 2016, through August 31, 2021, and were discharged home. Predicted probabilities of return visits for bleeding within 30 days were calculated to estimate quantiles for bleeding rates. A secondary analysis included logistic regression of bleeding risk by demographic characteristics and associated conditions. Data analyses were conducted from August 7, 2022 to January 28, 2023.Main Outcomes and MeasuresRevisits to the emergency department or hospital (inpatient/observation) for bleeding (primary/secondary diagnosis) within 30 days after index discharge after tonsillectomy.ResultsOf the 96 415 children (mean [SD] age, 5.3 [3.9] years; 41 284 [42.8%] female; 46 954 [48.7%] non-Hispanic White individuals) who had undergone tonsillectomy, 2100 (2.18%) returned to the emergency department or hospital with postoperative bleeding. The predicted 5th, 50th, and 95th quantiles for bleeding were 1.17%, 1.97%, and 4.75%, respectively. Variables associated with bleeding after tonsillectomy were Hispanic ethnicity (OR, 1.19; 99% CI, 1.01-1.40), very high residential Opportunity Index (OR, 1.28; 99% CI, 1.05-1.56), gastrointestinal disease (OR, 1.33; 99% CI, 1.01-1.77), obstructive sleep apnea (OR, 0.85; 99% CI, 0.75-0.96), obesity (OR,1.24; 99% CI, 1.04-1.48), and being more than 12 years old (OR, 2.48; 99% CI, 2.12-2.91). The adjusted 99th percentile for bleeding after tonsillectomy was approximately 6.39%.Conclusions and RelevanceThis retrospective national cohort study predicted 50th and 95th percentiles for posttonsillectomy bleeding of 1.97% and 4.75%. This probability model may be a useful tool for future quality initiatives and surgeons who are self-monitoring bleeding rates after pediatric tonsillectomy.