Purpose <p>We constructed a multinomial nomogram to predict postoperative hypocalcemia and hypercalcemia following parathyroidectomy (PTX) in dialysis patients with secondary hyperparathyroidism (SHPT).</p> Methods <p>We analyzed 685 dialysis patients undergoing PTX between January 2013 and May 2025. Patients were randomly allocated into a training cohort (<i>n</i> = 479) and a validation cohort (<i>n</i> = 206) in a 7:3 ratio. Independent predictors of postoperative calcium levels were identified using a multinomial logistic regression model. Model performance was internally validated using 200 bootstrap resamples and assessed by the area under the receiver operating characteristic curve (AUC), calibration curves, and decision curve analysis (DCA).</p> Results <p>Postoperative hypocalcemia occurred in 21.2% (<i>n</i> = 144) of patients, while 10.5% (<i>n</i> = 72) developed hypercalcemia. The final nomogram incorporated seven clinical variables: gender, dialysis duration, preoperative serum calcium, parathyroid hormone (PTH), alkaline phosphatase (ALP), C-terminal telopeptide (CTX), and intraoperative PTH (ioPTH). The nomogram demonstrated excellent discrimination, achieving a macro-AUC of 0.87 (95% CI: 0.84, 0.90) in the training set and 0.81 (95% CI: 0.76, 0.86) in the validation set. Calibration curves exhibited concordance between predicted probabilities and actual outcomes, and DCA confirmed that the model provides a clinical net benefit across probability thresholds of 0 to 0.45 for both abnormal calcium states.</p> Conclusions <p>This nomogram accurately stratifies the risk of bidirectional calcium disturbances in SHPT patients, empowering clinicians to optimize perioperative monitoring and individualized supplementation strategies.</p>