OBJECTIVES: To inform allocation decisions in any healthcare system, robust cost data are indispensable. Nevertheless, recommendations on the most appropriate valuation approaches vary or are nonexistent, and no internationally accepted gold standard exists. This costing analysis exercise aims to assess the impact and implications of different calculation methods and sources based on the unit cost of general practitioner (GP) consultations in Austria. *** METHODS: Six costing methods for unit cost calculation were explored, following 3 Austrian methodological approaches (AT-1, AT-2, AT-3) and 3 approaches applied in 3 other European countries (Germany, The Netherlands, United Kingdom). Drawing on Austrian data, mean unit costs per GP consultation were calculated in euros for 2015. *** RESULTS: Mean unit costs ranged from €15.6 to €42.6 based on the German top-down costing approach (DE) and the Austrian Physicians’ Chamber’s price recommendations (AT-3), respectively. The mean unit cost was estimated at €18.9 based on Austrian economic evaluations (AT-1) and €17.9 based on health insurance payment tariffs (AT-2). The Dutch top-down (NL) and the UK bottom-up approaches (UK) yielded higher estimates (NL: €25.3, UK: €29.8). Overall variation reached 173%. *** CONCLUSIONS: Our study is the first to systematically investigate the impact of differing calculation methods on unit cost estimates. It shows large variations with potential impact on the conclusions in an economic evaluation. Although different methodological choices may be justified by the adopted study perspective, different costing approaches introduce variation in cross-study/cross-country cost estimates, leading to decreased confidence in data quality in economic evaluations.