How accurate are people when predicting whether they will vote? These self-predictions are used by political scientists to proxy for political motivation, and by public opinion researcher to predict election outcomes. Phone surveys from three elections, including one survey experiment, are analyzed to compare respondents' pre-election vote intention with their actual voting behavior using administrative records (N=29,403). Unsurprisingly, many who predict that they will vote actually do not vote. More surprisingly, many who predict that they will not vote actually do vote (29% to 56%). Records of past voting behavior predicts turnout substantially better than self-prediction. Self-prediction inaccuracy is not caused by lack of cognitive salience of past voting, or by inability to recall past voting. Moreover, self-reported recall of turnout in one past election predicts future turnout just as well as self-prediction. We discuss implications for political science research, behavioral prediction, election administration policy, and public opinion.