The most common way to calculate your pregnancy due date is by counting 40 weeks from the first day of your last menstrual period LMP. And that's how most healthcare providers do it.
If your menstrual cycle length is the average length day cycle , your menstrual cycle probably started about two weeks before you conceived. This explains why pregnancies are said to last 40 weeks instead of 38 weeks.
This method doesn't take into account how long your menstrual cycle actually is or when you think you might have conceived.
But generally speaking, women typically ovulate about two weeks after their menstrual cycle starts. And women are more likely to know when their last period started than the day they ovulated.
If you do happen to know precisely when you conceived — say, if you were using an ovulation predictor kit or tracking your ovulation symptoms — you can calculate your pregnancy due date based on your conception date. Just choose that calculation method from the pulldown above and put in your date.
Note: Again, you don't necessarily conceive on the day you have sex. But for a fun read, see our stories from parents who know when and where they did the deed that resulted in their child.
If you had a Day 5 embryo transfer, count days from your transfer date. If you had a Day 3 embryo transfer, count days. Your healthcare provider might revise your due date if your baby is measured during a first trimester ultrasound scan and found to be much bigger or smaller than expected for gestational age.
This is more likely to happen if you have an irregular menstrual cycle length that makes it hard to pinpoint the date of conception. Your healthcare provider will measure your baby during that ultrasound exam to figure out how far along your baby is and then provide you with a new due date.
If you already know your due date, you can use this calculator to see your pregnancy calendar. It will tell you when you'll hit various milestones, like when your baby's heart starts beating, and when you may be due for prenatal tests and prenatal care.
You'll also find what your baby's sign and birthstone will probably be and which famous people were born on your due date. Of course, a due date calculation is always approximate, whether it's from our tool or from your doctor or midwife. Only 1 in 20 women delivers on her due date. You're just as likely to go into labor any day during the two weeks before or after. Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination.
Am J Obstet Gynecol. PMID 7. Birth weight from pregnancies dated by ultrasonography in a multicultural British population. Sep 4 ; PMID 8. Ultrasonography in Pregnancy. American College of Obstetricians and Gynecologists. Conceptional age, menstrual age, and ultrasound age: a second-trimester comparison of pregnancies of known conception date with pregnancies dated from the last menstrual period. PMID: Trauma in pregnancy. Emerg Med Clin North Am. Hay DL, Lopata A. Chorionic gonadotropin secretion by human embryos in vitro.
J Clin Endocrinol Metab. Wilcox AJ, et al. Time of implantation of the conceptus and loss of pregnancy. N Engl J Med. Lohstroh P, et al. Daily immunoactive and bioactive human chorionic gonadotropin profiles in periimplantation urine samples. Biol Reprod. Cervical insufficiency.
The American College of Obstetricians and Gynecologists. Berghella V, et al. Ultrasound Obstet Gynecol ; ACOG practice bulletin. Prevention of Rh D alloimmunization. Number 4, May replaces educational bulletin Number , October Clinical management guidelines for obstetrician-gynecologists.
American College of Obstetrics and Gynecology. Int J Gynaecol Obstet. Fetal Lung Maturity. Antepartum fetal surveillance. Institute for Clinical systems Improvement. Routine Prenatal Care. Home Pregnancy. Due date calculator March, What was the first day of your last period?
Have you been trying to work out your pregnancy due date and found yourself adding, subtracting, multiplying and counting on your fingers? It can be confusing, whether your baby is due 34 or four weeks from today! Luckily, our handy pregnancy due date calculator can help you easily find out when your baby is due. How is my pregnancy due date calculated?
Unless you've been tracking your ovulation, there's no way to know for sure exactly when you ovulated and conceived. That's why your due date is calculated based on the date of your last period instead. Most women ovulate about two weeks after the first day of their period, and conceive shortly afterwards.
The average pregnancy lasts between 37 weeks and 42 weeks. Our calculator uses this information to give you an estimated due date. Will my baby definitely be born on my due date? Unfortunately, no one can say for sure exactly when your baby will arrive.
In fact, only about four per cent of babies are born on their due date! But it is likely that your baby will arrive in the few weeks either side of your estimated due date. Knowing this can help you to be prepared for labour and birth, and to have everything ready for your new baby. Will my due date change when I have a scan? It may do. Your first pregnancy scan will probably happen when you're between 10 weeks and 14 weeks pregnant.
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