To test the influence of relationship length on ability to predict a partner's preferences, 58 younger (M = 24.1 years) and 20 older (M = 68.7 years) couples made predictions in three domains that varied in daily importance. While prediction accuracy was generally better than chance, longer relationship length correlated with lower prediction accuracy and greater overconfidence. The difference in accuracy between older and younger couples increased for strong preferences and when controlling for preference reliability over time. Independent of relationship length, prediction accuracy was higher for important domains, for strong, reliable, and stereotypical preferences, and when couples were more similar.