Although research on mental accounting and reason based choice has been extensive,scholars have concentrated on mental accounting phenomena from the perspective of the individual on decisions that affect only the individual.We propose that,due to the importance of fairness & equity within a marriage as well as being able to label a spouse as a money source,many of the mental accounting principles that hold true for individuals,do not hold true for marriages.Our studies show that when applying prior rules of mental accounting to windfall gains or allocation of money within a marriage,results are not consistent with reality,and our study provides new mental accounting principles to account for real marital behavior.