Conception Calculator Conception Calculator Track your fertile window and future pregnancy milestones. First Day of Last Period (LMP) JanuaryFebruary MarchApril MayJune JulyAugust SeptemberOctober NovemberDecember Average Cycle Length (Days) Calculate Primary Conception Date - Probable Window: - Next Period - Due Date (If Pregnant) - Next 3 Cycles Forecast Cycle Period Date Conception Fertile Window Due Date