Time-activity data are traditionally collected by telephone interviews or through paper diaries, which are time consuming and costly. As a potential alternative that may greatly save staff time, a web survey to collect time-activity data was developed and tested in this study. We collected 24-h recall web diaries from 151 parents of young children mostly under 55 years of age (who also answered for their children) and 55 older adults (≥ 55 years of age) both on a weekday and a weekend day every 3 months during an 18-month period. The performance and reliability of the web surveys collected were evaluated, including the survey-completion rate, and the percentage of surveys with unreasonable time being reported as spent sleeping and with missing reports of being in transit between locations. We also compared the web-survey data with time-activity information we collected from the same subjects in telephone interviews and found that these data sources were fairly consistent with each other. However, we observed slightly more compliance issues for the web than the telephone survey, but most of these issues could be addressed and minimized by refining some questions or the survey interface. Our study suggests that it is critical to reduce participants' burden and improve survey interface design for optimal compliance and data quality. In conclusion, web surveys are a promising method to consider for time-activity data collection.