Calendar instruments incorporate aided recall techniques such as temporal landmarks and visual time lines that aim to reduce response error in retrospective surveys. Those calendar instruments have been used extensively in off-line research (e.g., computer-aided telephone interviews, computer assisted personal interviewing, and paper and pen interview) and have been shown to increase the quality of retrospectively collected life course data. The goal of our study was to investigate if calendar recall aids can also improve data quality in web surveys. In a methodological field experiment, we evaluated the effects of adding visual feedback and personal landmarks to our questionnaire with regard to response/break off rates, completeness of retrospective reports, interview duration, and respondent evaluations. The study included 1,451 respondents from a probability-based Internet panel who were randomly assigned to one of the four conditions of the experiment. The results indicate that in the web-based calendar tool, visual feedback properties exerted the most influence on data quality.