Background With the advent of modern imaging technologies, non-invasive assessment of the coronary system is not only possible but its complexity and plaque burden can be quantified. This study aims to determine whether calcium score on computed tomography coronary angiography (CTCA) can be associated with the complexity of coronary artery disease (CAD), which is determined by the SYNTAX score on coronary angiography, as well as to determine which cut-off value of coronary artery calcium (CAC) score can predict severe CAD in our population. Methodology This was a cross-sectional study conducted at the Rawalpindi Institute of Cardiology, Pakistan from January 2019 to March 2020. The calcium score of all patients with low-to-intermediate pretest probability of CAD was calculated on CTCA. All patients who had significant disease on CTCA were subjected to conventional coronary angiography and SYNTAX score was calculated, which was later used to determine the association between calcium and SYNTAX score. Results A total of 90 patients were included in the study. CAC and SYNTAX score were found to be positively correlated (Pearson coefficient [r] = 0.354; p = 0.001). The total CAC score with a cut-off value of 212 recognized patients with the SYNTAX score of >27. The sensitivity was 66.7% and specificity was 70.5% with an area under the curve of 0.743. The mean calcium score of patients in our study group was 223, with the maximum score of 1,216 and the minimum score of zero. Conclusion A CAC score greater than 212 is associated with a high SYNTAX score indicating complex disease. Only age is an independent predictor of calcium score.