On the basis of a post-election questionnaire survey and self-reported voter motivations analysis, this article explores the extent, forms, and determinants of tactical voting in the 2021 Czech parliamentary elections. The prevalence of tactical voting was estimated to be approximately 15%. A significant portion of the electorate harbored a strong aversion towards the ANO political party and its leader, Andrej Babiš. Consequently, regardless of their political preferences, these voters opted for SPOLU, the party with the best chance of defeating him. This strategic approach significantly influenced the election results, including having an impact on the overall winner. According to the binary logistic regression model, younger individuals and those with higher levels of education inclined more towards tactical voting. These findings correspond with studies from different countries, confirm the socio-demographic conditionality of tactical voting, and contribute to the wider discussion of this concept in proportional representation systems.