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Pregnancy Week Calculator

Calculate how many weeks and days pregnant you are today (or on any as-of date) from your last menstrual period. Also shows gestational month, trimester and due date.

Input

Counting starts from the first day of your last menstrual period (the day your period began) as week 0, day 0. The as-of date defaults to today.

YYYY/MM/DD
YYYY/MM/DD

Result

Enter the first day of your last menstrual period.

How it works

  • Gestational age is counted using the standard obstetric method, treating the first day of the last menstrual period (LMP, the day your period began) as week 0, day 0. The number of elapsed days divided by 7 gives the weeks, and the remainder gives the days.
  • The gestational month is converted as 4 weeks = 1 month and shown from month 1 to 10. The trimester is divided as up to 13 weeks for the first trimester, 14 to 27 weeks for the second, and 28 weeks onward for the third.
  • The due date is calculated with Naegele's rule by adding 280 days (40 weeks, 0 days) to the first day of the last menstrual period. If your cycle is not 28 days or ovulation is shifted, the actual due date may differ.
  • The as-of date defaults to today. Change it to any date to check how many weeks you were (or will be) on a past or future date.
  • Because of how counting works, the first day of the last menstrual period is week 0, day 0, and the time of your next expected period falls around week 4. Your actual gestational age and due date are confirmed by a doctor based on ultrasound (fetal size) and other measurements.
  • This tool is a general estimate using a common formula and is not a diagnosis or medical advice. Always consult a doctor for health decisions.