It is shown how the time limit on a test can be set to control the probability of a test taker running out of time before completing it. The probability is derived from the item parameters in the lognormal model for response times. Examples of curves representing the probability of running out of time on a test with given parameters as a function of the time limit are presented. Unlike the traditional methods of dealing with test speededness, which assess the degree of speededness after the test has been administered, the curves enables us to set a desired degree in advance. The method is demonstrated using an empirical data set.