Purpose:The Weekly Calendar Planning Activity is a performance test aiming to examine how subtle problems with executive functioning influence the performance of multi-step activities in daily life. The purpose of this study was to explore the Swedish version of the Weekly Calendar Planning Activity, regarding test-retest reliability and possible learning effects. Material and methods:Twenty-four adults with psychiatric, neurodevelopmental or mild intellectual disorders and with difficulties in executive functioning performed the test on three separate occasions, with two weeks apart. Test-retest reliability was determined using intraclass correlation coefficients. Possible learning effects were evaluated. The smallest detectable change was calculated to determine the precision of individual scores. Results and conclusion:The intraclass correlation coefficients between the first two test occasions were weak (0.42-0.66), but were acceptable to excellent (0.65-0.91) between test occasions 2 and 3. There was a considerable amount of random variation in the results, but little systematic variation, indicating no or possibly a small learning effect in the total number of accurately recorded appointments. This variation indicates a need to use two consecutive baseline measurements when the Swedish version of the Weelky Calendar Planning Acitivity is used as an outcome measure. Together, our results suggest that the Swedish version of the Weelky Calendar Planning Acitivity is a useful performance-based measure of how subtle problems in executive functioning affects activity performance.