The 2017 American blood pressure (BP) guidelines recommended a personalized risk-based approach to treatment in stage 1 hypertension. We sought to establish the utility of coronary artery or thoracic aortic calcium (CAC or TAC) as additional risk modifiers in this setting. We included 1859 Multiethnic Study of Atherosclerosis participants with stage 1 hypertension. We compared adjusted HR for the composite outcome of incident atherosclerotic cardiovascular disease or heart failure across predefined categories of either CAC or TAC (0, 1 to 100, or >100) in: (1) the full sample; (2) 4 high-risk subgroups recommended for pharmacotherapy to a BP goal <130/80 mm Hg, and (3) low-risk subgroup not eligible for pharmacotherapy. We also estimated the 10-year number-needed-to-treat (NNT10) to a systolic BP <130 mm Hg as extrapolated from meta-analyses. Mean age was 62.8 ± 9.4 years, 46% were female and there were 300 events over a median follow-up of 13.8 years. The absolute event rate was 4.1 to 10.8 per 1,000 person-years among high-risk participants with CAC = 0, but 28.4 among low-risk participants with CAC >100. CAC >100 was independently associated with a higher relative risk of events compared with CAC = 0 (e.g., adjusted HR [9.5 (1.8 to 18.7)] in the low-risk subgroup). NNT10 for CAC = 0 were 3 to 5 times higher than those for CAC >100 in all analyses. TAC was not a reliable risk modifier in our study. In conclusion, CAC, but not TAC, can further guide risk-based allocation of treatment in stage 1 hypertension and should be considered as a risk modifier in future guidelines.