Election forecasts can be improved by adding wisdom-of-crowds questions to election polls. In particular, asking people about the percentage of their social contacts who might vote for different political options (social-circle question) improved predictions compared to traditional polling questions about participants’ own voting intentions in three recent U.S. elections (2016, 2018, and 2020) as well as in three recent elections in European countries with larger number of political options (in 2017 French, 2017 Dutch, and 2018 Swedish elections). Using data from large national online panels, we investigate three reasons that might underly these improvements: an implicitly more diverse sample, decreased social desirability, and anticipating social influences on how people will vote. Another way to use wisdom of crowds is asking people to forecast who will win the election (election-winner question). We find that the social-circle question can be used to select individuals who are better election-winner forecasters, as they typically report more diverse social circles. A combination of social-circle, election-winner, and traditional own intention questions has performed best in 2018 and 2020 U.S. elections. Taken together, our results suggest that election polling can produce accurate results when traditional questions are augmented with wisdom-of-crowds questions.