Aims: Accidental parathyroidectomy is a major cause of post-thyroidectomy hypoparathyroidism, affecting recovery and long-term calcium management. Despite this, predictors of inadvertent parathyroid removal are not routinely incorporated into operative planning. This study aimed to identify risk factors for accidental parathyroidectomy in total thyroidectomy and develop a practical risk-stratification model to anticipate postoperative hypoparathyroidism. Methods: A retrospective cohort study was conducted on patients undergoing total thyroidectomy across three Australian tertiary centres (2010–2020). Clinical variables were analysed using Chi-square/Fisher’s exact tests, with multivariable logistic regression used to identify independent predictors. These informed a risk-stratification tool based on pre- and intra-operative factors. Results: Among 295 patients, accidental parathyroidectomy occurred in 26% (78/295). Inadvertent gland removal significantly increased temporary hypoparathyroidism (OR 3.1; P<0.001) and permanent hypoparathyroidism (OR 17.75; P=0.04). Malignancy (OR 1.91; P=0.015) and central lymph node dissection (OR 4.94; P<0.001) were the strongest predictors, with auto-transplantation also associated with postoperative hypocalcaemia. Risk-prediction tables were developed, showing maximal risk in malignant disease requiring central neck dissection: 59.5% for accidental parathyroidectomy and 74.1% for temporary hypoparathyroidism. Any central neck dissection conferred >50% risk, and auto-transplantation raised risk above 40%. Conclusions: Accidental parathyroidectomy is common and strongly associated with malignancy and central lymphadenectomy. The resulting risk-stratification model provides a practical framework to predict postoperative hypoparathyroidism, guide peri-operative counselling, and support tailored postoperative calcium and vitamin D management.