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Find Your Due Date

How is my due date calculated?

There are several ways. If you happen to know the day you conceived, you can count 38 weeks from that day to find your due date. (Human gestation takes about 38 weeks.)

But very few expectant moms know exactly when they conceived. Even if you only had sex once during your fertile period, you wouldn't conceive on that day unless you happen to be ovulating. Sperm can live for up to five days inside your fallopian tubes. So, it could be up to five days after you have sex that you release an egg (ovulate) and it gets fertilized by a waiting sperm. That's the day you conceive. 

So without knowing the day of conception, how does anyone determine a due date?

First day of your last period

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 (28-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.

Conception date

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.

IVF transfer date

If you conceived through IVF, you can calculate your due date using your IVF transfer date. If you had a Day 5 embryo transfer, count 261 days from your transfer date. If you had a Day 3 embryo transfer, count 263 days.

Can my due date change?

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.

What if I already know my 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.

How likely am I to give birth on my 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.

In The Know

The Real Myths & Facts

Coffee could cause a miscarriage.

False. But that doesn’t mean you can java your way through the day. “Caffeine does cross the placenta, so less than 200 milligrams of caffeine daily is recommended,” says Dr. England.

That’s a little more than the amount in a cup of coffee, which is eight ounces. And size matters. A short Starbucks® coffee has 180 mg, while a Venti crams in 475 mg.

Other sources of caffeine matter, too. Red Bull has 10 mg per oz., while just 2 ounces of 5-Hour Energy tops out your day’s total. A Starbucks Chai Latte Grande has 95 mg, while most bottled teas have around 40 mg. A 12 oz. can of soda typically has around 45 mg.

“It’s important to look at package ingredient lists, which can be found online,” Dr. England says.

Your feet will expand.

True. Sadly, feet widen and swell during pregnancy. Pregnancy may not be the best time to buy those Jimmy Choos and Christian Louboutins.

“Each foot has 26 bones and over 30 joints that are held together with ligaments. Just like the ligaments in your pelvis, that connective tissue relaxes, due to hormones,” Dr. England says. “Weight gain also contributes, as does swelling in the third term.”

You can help your feet with cardiovascular exercise, compression hose and pregnancy massages. Also elevate your feet when possible.

Dying your hair will endanger your baby.

False. The dye itself won’t endanger you or your baby, but you should sit in a well-ventilated area and turn on a fan, to make sure you have fresh air to breathe. The fumes of dye and bleach could make you faint or become nauseous in the beginning of pregnancy, especially if your blood pressure is low.

Hot baths are harmful.

True. They’re risky, and hot tubs or whirlpools can double your chance of miscarriage, as a late 1990s study found. Also avoid saunas. But steamy showers are fine and warm baths might be OK, though if you’re prone to yeast or bacterial infections, a bath might further irritate that body area. “Another concern for baths is women’s blood pressure can be low during early pregnancy, making them dizzy and raising risk for fainting,” she says. “Your Ob/Gyn can advise you on your personal risk.”

You can bank on your due date and deliver nine months to the day after conception.

False. Alas, pregnancy typically lasts 40 weeks, technically just over nine months. “Nine months, or 36 weeks, is considered a preterm birth,” says Dr. England.

Don't swim in public pools.

True. You cannot drown your baby since water cannot enter the amniotic sac. But germs can, so you could pick up a harmful infection. “Some kiddos urinate in community pools,” Dr. England says. “If your friend has a pool, it’s easier to assess whether it’s safe.”

Walking or spicy foods will induce labor.

False. Walking, intercourse or spicy foods won’t bring on baby or shorten labor. The drugs pitocin, cervidil and misoprostol, however, will. So can a cervical balloon catheter.

“Even then, it might take one to two days to reach active labor,” she says. “I always counsel patients that this is a marathon, not a sprint. You cannot snap your fingers and have a baby right away.”

Cat litter causes birth defects.

True. It can, since the parasite toxoplasmosis sometimes found in feline feces could be transmitted to your fetus. Your baby could be stillborn, grow poorly in the womb or have excess fluid collect in the brain, known as hydrocephalus. Epilepsy, blindness, cerebral palsy or too-small brains are dangers from contamination. “You don’t need to give away your cat. Instead ask someone else to change the litter box,” she says. Consider that a pregnancy perk.

It's dangerous to exercise.

False. Other than hot yoga, working out helps mom and baby during pregnancy, especially if you exercised before. Check with your doctor, if you’re concerned about miscarriage or preterm birth.

“We caution against hot yoga because you might faint,” says Dr. England.

New exercisers can safely walk briskly 30 minutes daily. If Texas’ torrid temps make you uncomfortable, walk on a treadmill or at a mall.

You never should sleep on your back.

True. “Doctors recommend against sleeping on your back during the second and third trimester because the entire weight of the baby presses on your back and the vena cava, the main blood vessel that returns blood to your heart from the lower body. This may cut blood flow to the baby, and along with it oxygen and nutrients.

That does you no favors either by aggravating backaches, hemorrhoids, dizziness and ankle/feet swelling. “That’s why we recommend sleeping on your side–if possible the left side. That increases blood flow to the baby,” says Dr. England.

If you wake up on your back, don’t panic, just switch to your side.

You cannot get pregnant while nursing.

False. If you breastfeed, you may have no periods, but you still can ovulate. Your age, frequency and length of nursing can lead to infertility—but there’s no guarantee.

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