In order to estimate the likely effects on item difficulty when a calculator becomes available on the quantitative section of the Graduate Record Examinations® (GRE®-Q), 168 items (in six 28-item forms) were administered either with or without access to an on-screen four-function calculator. The forms were administered as a special research section at the end of operational tests, with student volunteers randomly assigned to the calculator or no-calculator groups. Usable data were obtained from 13,159 participants. Test development specialists were asked to rate which items they thought would become easier with a calculator. In general, the specialists were successful in identifying the items with relatively large calculator effects, though even these effects were quite small. An increase of only about four points in the percent correct should suffice for the items identified as likely to show calculator effects with no adjustment needed for the majority of the items. Introduction of a calculator should have little or no effect on gender and ethnic differences.