Do people have biased perceptions of their political orientation? Based on the link between political conservatism and in-group loyalty, we predicted that people would underestimate their liberalism and that this effect would be more pronounced among political conservatives. Young adults indicated their self-perceived political orientation and completed an objective measure of political orientation, which placed them along a liberal-conservative continuum by comparing their attitudes on 12 core issues (e.g., gay marriage, welfare) to population norms. Participants showed a significant bias toward perceiving themselves as more conservative than they actually were, and this effect was more pronounced among independents and conservatives than liberals. Further, biased self-perceptions of political orientation predicted voting behavior in the 2012 Presidential Election after controlling for objective political orientation scores. Discussion highlights theoretical implications for self-knowledge research and practical implications for American politics more broadly.