Background 10-15% of patients with gallstone related pathology have choledocholithiasis, with endoscopic retrograde cholangiopancreatography (ERCP) being a treatment option. Spontaneous passage of common bile duct (CBD) stones not infrequently result in negative ERCPs with unnecessary procedural risks and resource utilisation. To reduce this, we aim to derive predictors for spontaneous stone passage. Methods We performed a single centre, retrospective cohort study at St John of God Midland Hospital in Western Australia, Perth on 78 patients who underwent ERCP following imaging confirmed choledocholithiasis from June 2022 – Sep 2024. Multivariable logistic regression models were used to analyse predictors for spontaneous stone passage. Receiver Operating Characteristics (ROC) curve and Youden Index were used to investigate if the drop in liver function test (LFT) indices from initial diagnosis of choledocholithiasis to just prior to ERCP can predict spontaneous stone passage. Results 21.5% of patients with imaging proven choledocholithiasis had no evidence of stones on ERCP, suggestive of interval spontaneous passage. Size of CBD stone was independently associated with spontaneous stone passage. For each 1mm increase in stone size, the odds of spontaneous passage decreased by 54% (adjusted OR 0.46, 95% CI 0.27–0.77; p=0.003). Among the 5 biochemical predictors evaluated (bilirubin, AST, ALT, ALP, GGT), the drop in ALT from initial choledocholithiasis diagnosis to just prior to ERCP demonstrated a fair diagnostic performance with an area under curve (AUC) of 0.708 (95% CI: 0.548-0.868). At the optimal ALT cutoff of 210.5 U/L, the test achieved moderate sensitivity (70.6%) and moderate specificity (74.2%) in predicting spontaneously passed stones, resulting in a Youden Index of 0.448. Conclusion 1 in 5 CBD stones will likely pass spontaneously. For patients with a small CBD stone and ALT drop of 210.5 U/L, repeat imaging could be considered prior to ERCP for reassessment.