How to Calculate My LMP

For women, determining their LMP (last menstrual period) may seem like an intimidating task. However, calculation of LMP is fairly simple and can be beneficial for multiple reasons. Calculating LMP is the most common method for determining a pregnant woman's due date. For women who have inconsistent menstrual cycles or ovulation, their LMP can keep them informed about their body and give important information to their health care provider. LMP specifically refers to the first day of a woman's menstrual cycle.

Instructions

    • 1

      Look at a calendar to determine the last time your menstrual cycle began. Try to be as accurate as possible. The first day of menstrual bleeding should count as Day 1 of your cycle. Any spotting that happens before actual menstrual flow typically is not considered the first day of your cycle.

    • 2

      Mark the first day of your last menstrual cycle on a calendar. This date is your LMP.

    • 3
      If you are pregnant, the LMP calculation method can help determine your due date and the gestational age of your baby.

      Continue to mark the first day of each menstrual cycle on the calendar to maintain a current calculation of your LMP.

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