Handheld calculators have been used on the job for more than 30 years, yet the degree to which these devices can affect performance on employment tests of mathematical ability has not been thoroughly examined. This study used a within-subjects research design (N = 167) to investigate the effects of calculator use on test score reliability, test score validity, and test performance as well as the possible moderation of these effects across different types of tests, numbers, and arithmetic operations. Results indicate that total test scores maintained reliability and validity in the calculator condition regardless of test type. However, calculator use disrupted the measurement of mathematical skill when items were composed of integers and decimals, but not of fractions, and this disruption depended on the arithmetic operation required by the item. Nonetheless, the findings suggest that selection specialists may allow job applicants to use calculators on standardized math tests that have an adequate diversity of items without compromising the accuracy of the obtained total test scores. (Contains 8 tables and 3 figures.)