The mental accounting of sunk time costs: why time is not like money

Abstract The sunk‐cost effect, an irrational attention to non‐recoverable past costs while making current decisions, has been documented widely in the domain of monetary costs. In this paper, I study the effect of past time investments on current decisions. In three experiments using choice situations, I demonstrate that the sunk‐cost effect is not observed for past investments of time, but the effect reappears when the investments are expressed as monetary quantities. I further propose that this ‘pseudo‐rationality’ is due to the fact that individuals lack the ability to account for time in the same way as they account for money. In two additional experiments, I facilitate the accounting of time and show that the irrational sunk‐cost effect reappears. In a final experiment, I test my propositions in a setting where subjects make real investments of time and subsequently make real choices. Copyright © 2001 John Wiley & Sons, Ltd.