What Is LMP?

Pregnancy Weeks Calculator

Enter the first day of your last menstrual period (LMP) to see how many weeks and days pregnant you are today. Pregnancy is conventionally counted from that date.1

Updated October 2, 2026 · Your date stays on your device

How many weeks pregnant am I?

The day your last period started (the first day of bleeding), not the day it ended. The calculator counts to today's date on your device.

What pregnancy weeks mean

How far along a pregnancy is, its gestational age, is described in weeks and days counted from the first day of the last menstrual period.1 A typical pregnancy is about 40 weeks counted this way.2

Because the count starts on the first day of the LMP, it begins before conception would normally happen. The standard convention assumes ovulation on day 14 of a 28-day cycle,3 so conception is assumed to happen about two weeks after the first day of the LMP.1 At conception, a pregnancy is therefore already counted as about two weeks along.

Read how pregnancy weeks are counted

How the calculator works

The calculator counts the calendar days from the first day of your LMP to today's date on your device. The LMP day itself is 0 weeks, 0 days. Every 7 days make one completed week, and the days left over are shown as days.

Worked example

First day of the LMP: August 1, 2026. Today: October 2, 2026.

That is 62 days: 8 completed weeks (56 days) plus 6 days, so 8 weeks, 6 days.

The result uses only the date you enter and today's date. It does not adjust for cycle length or use any other dating information.

Why the result is an estimate

An LMP-based count depends on the LMP date being right. The convention does not account for an LMP that is remembered inaccurately, for cycles of irregular length, or for ovulation that happens earlier or later than usual.3 ACOG notes that about half of women are reported to recall their LMP accurately.3

Talk with your doctor or midwife if you are not sure of the first day of your last period, if your periods are irregular, or if you have been given different dates. A due date first worked out from the LMP may be changed after a dating scan.4 This site cannot interpret your scans or records.

Back to What Is LMP?

Sources

  1. American College of Obstetricians and Gynecologists (ACOG). How Your Fetus Grows During Pregnancy. patient FAQ, reviewed 2026.
  2. American College of Obstetricians and Gynecologists (ACOG). Definition of Term Pregnancy (Committee Opinion No. 579). 2013; reaffirmed 2025.
  3. American College of Obstetricians and Gynecologists (ACOG). Methods for Estimating the Due Date (Committee Opinion No. 700). 2017; reaffirmed 2025.
  4. NHS (England). Ultrasound scans in pregnancy. reviewed November 2023.