Last Menstrual Period

Last menstrual period (LMP) refers to the start date of the most recent menstrual period. A typical menstrual cycle is around 21-35 days in length, with the first day of bright red menstrual bleeding signifying day 1 or the start of the cycle.

For example, if the first day of bright bleeding in a most recent menstrual cycle occurred on January 1st, the LMP would be January 1st.