The aim of the present study was to determine the percentage of infertility patients who are diagnosed with a non-receptive endometrium according to the endometrial receptivity array (ERA) test and to examine whether adjusting the embryo transfer day according to the proposed shift in the window of implantation improves the pregnancy rate compared to non-ERA-tested patients.A single-center retrospective cohort study, including 53 consecutive good prognosis patients (0-2 previous frozen embryo transfers) admitted to our IVF unit for a mock cycle prior to their frozen day-5 embryo (blastocyst) transfer cycle. The mock cycle included an endometrial biopsy for both the ERA test and histological assessment by the Noyes criteria (study group). The next cycle frozen embryo transfer (FET) in the study group was adjusted according to the ERA results. The control group consisted of patients who underwent FET cycles at our clinic during the same period, without performing the endometrial biopsy and ERA testing.During the study period, 503 patients (control group) underwent FET cycles without performing the ERA testing and 41 patients had FET following an ERA test. There were no between-group differences in patients' age, number of previous transfers, endometrial thickness, number of transferred embryos, and ongoing pregnancy rates (35.2 vs. 39%, respectively, p = NS). Out of the 53 patients who performed the ERA test before their first or second FET, five endometrial samples (9.4%) were found to be post-receptive, 29 (54.7%) pre-receptive, and only 19 samples (35.8%) were receptive. Women in the study group with pre- or post-receptive endometrium on ERA testing, the appropriate adjustment in timing of FET according to the ERA test resulted in a 33.3% pregnancy rate, which is comparable to the 35.2% background ongoing pregnancy rate of the control group.Performing the ERA test in a mock cycle prior to a FET does not seem to improve the ongoing pregnancy rate in good prognosis patients. Further large prospective studies are n...