This paper reports a comparison of the Austrian National Household Travel Survey (HTS) and Time Use Survey (TUS) with a 3^rd survey format - the "Mobility-Activity-Expenditure-Diary" - to better understand the specific strengths and weaknesses of HTS and TUS in terms of quantifying travel and non-travel activities and their specific underreporting effects. The main goal is to demonstrate how reliable we can infer from both survey types on travel and non-travel activities regarding different indicators.