Abstract: A calendar providing an indication of the period of time in which a woman is most likely to conceive during a calendar month. The calendar includes an inner wheel rotatably attached to an outer wheel. The inner wheel includes markings indicating the relevant points of a woman's cycle to include the start of a woman's menstrual period and an at-risk phase. The outer wheel includes markings for a conventional calendar. The user aligns the start of her period with the appropriate day of the month. The user may then determine when her at-risk phase begins. During this at-risk phase, the user is most likely to conceive if engaging in sexual intercourse. The calendar is portable and may include an optional locking device for locking the aligned inner wheel against the outer wheel.