Cyclical variations in women’s attractiveness have been hypothesized, suggesting that cues of fertility are displayed in, for instance, body odors, faces or behaviors. However, contradictory findings have been reported, with conclusions for and against this hypothesis. One of the likely explanations for this lack of consensus is the methodology used to determine the fertile phase of women’s cycle. The aim of this article is to compare two methods: estimation based on women’s self-reports versus detection of LH peak with urinary tests. This was performed on a sample of 23 women during a study on body odor attractiveness. The results showed that estimating the fertile phase using verbal reports only (backward counting method) was subject to a margin of error of at least 26%. The level of error was minimal at days 14 and 15 before the estimated start of the next menses, but may increase if the cycle is anovulatory. Although accuracy to spot women’s fertile phase is better when using LH peak detection with a urinary test, it is also more costly (in money and time) and constraining for both the experimenter and the participant.