Counterfactual thinking involves imagining hypothetical alternatives to reality. Philosopher David Lewis argued that people estimate the subjective plausibility that a counterfactual event could have occurred by comparing an imagined possible world in which the counterfactual statement is true against the current, actual world in which the counterfactual statement is false. Accordingly, counterfactuals considered to be true in possible worlds comparatively more similar to ours are judged as more plausible than counterfactuals deemed true in possible worlds comparatively less similar. However, the use of comparative similarity as a strategy for evaluating the perceived plausibility of counterfactual thoughts has not been the subject of psychological research. Instead, extant research has focused on factors such as ease of simulation, norm deviation or repetition. In this talk I offer empirical evidence suggesting that comparative similarity is a promising model for understanding how people assess counterfactual plausibility.