What is my last menstrual period?
Your last menstrual period is the first day of your last menstrual period.
- You can calculate your due date by adding 40 weeks (280 days) to your LMP.
- This is considered an accurate method of dating pregnancy since your date of conception is difficult to confirm.
Why is pregnancy dated from LMP when I wasn’t pregnant yet?
You weren’t pregnant those first two weeks; however, we can’t know for sure what day you conceived. Your LMP provides a more reliable marker for the start of pregnancy if you have a regular menstrual cycle.
What if I don’t know my LMP?
This dating method assumes that you have a regular, 28-day menstrual cycle where ovulation occurs on day 14.
- If you have irregular periods, your provider can determine your due date with an ultrasound.
- If you’ve been tracking ovulation symptoms or using ovulation strips, you can also add 266 days to your estimated ovulation day to get your due date.
Think you might be pregnant?
We provide free pregnancy tests and limited obstetrical ultrasounds (up to 20 weeks) here at The Pregnancy Network. Staff RNs can confirm your pregnancy with a medical-grade test, give you a limited obstetrical ultrasound, and discuss your pregnancy options with you. Our staff of licensed registered nurses is here for you.
Adrienne Bergmeier
Adrienne Bergmeier is a Communications Coordinator at The Pregnancy Network.