<p>Risk factors for cancer, such as ionizing radiation or chemical exposure, can be managed using risk-based approaches when clearly defined thresholds are absent. When considering different magnitudes of risk, it is crucial to use the same indices and calculations to conduct proper comparisons. This study quantified the annual excess probability of cancer-related mortality by attained age for continuous occupational exposure to ionizing radiation or inorganic arsenic (during a working period at ages between 18 and 64 years), using a calculation method recommended by the International Commission on Radiological Protection. Calculations were conducted as a case study using the occupational exposure limits (OELs) in Japan from the Japanese population data. These calculations provided information regarding the age-dependent probability of excess annual mortality from exposure to inorganic arsenic. Excess lifetime mortality probability was also calculated based on the probability of the excess annual mortality. Notably, previous direct risk comparisons between the cancer-related risks associated with radiation and inorganic arsenic exposure should be interpreted with caution, because uncertainties and differences in risk models and regulatory approaches related to OELs were not considered in many of these comparisons. The present study provides basic information for conducting risk comparisons between radiation and chemicals. The results obtained should support the development of well-balanced regulations for radiation and chemicals, from a holistic point of view.</p>