We are biased towards thinking that people are telling the truth. Our study represents the first test of how beliefs about the base rate of truths and lies affect this truth bias. Raters were told either 20, 50 or 80% of the speakers would be telling the truth. As the speaker delivered their statement, participants indicated moment by moment whether they thought the speaker was lying or being truthful. At the end of the statement, they made a final lie–truth judgment and indicated their confidence. While viewing the statement, base rate beliefs had an early influence, but as time progressed, all conditions showed a truth bias. In the final judgment at the end of the statement, raters were truth biased when expecting mostly truths but did not show a lie bias when expecting mostly lies. We conclude base rate beliefs have an early influence, but over time, a truth bias dominates. Copyright © 2014 John Wiley & Sons, Ltd.