Cost estimation not only requires precise technical and analytical input from estimators but also involves the use of subjective judgement. An investigation on the impact of stress on estimation performance was conducted involving 177 professional estimators in Hong Kong. Using correlation analysis, regression analysis and structural equation modelling, the relationships between stress and various aspects of estimation performance are examined and a causal structural model is developed. The results indicate that stress is a cause of negative estimation performance (resulting in weak interpersonal relationships, unfamiliarity with organization and ineffective process), while, simultaneously, it is beneficial to the professional estimation performance. Furthermore, there is an inverted U‐shaped relationship between stress and the organizational relationship.