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To use Mother&Baby's due date calculator you simply need to work out the first day of your last period and roughly how many days your menstrual cycle is (the average cycle is 28 days). The tool will calculate 40 weeks from the first day of your last menstrual period, even though your baby is technically about two weeks younger than that.
Unless you can pinpoint exactly what point of your ovulation cycle you were in at the time of fertilisation, it’s difficult to know what date exactly you’ll meet your little one. However, the pregnancy calculator can give you a good estimate.
Only about 4% of babies are born on their due date. Although this tool can give you a rough guide of when to expect your baby, we know all too well that baby will arrive when he is good and ready.
Most women ovulate and conceive two weeks after their last period (or LMP for Last Menstrual Period in fertility speak) and will only be around 38 gestational weeks by the time the pregnancy has reached the 40-week mark.
‘Your dating scan, which you’ll have at 10 to 14 weeks is the most accurate scan to determine your due date,’ explains Teresa Walsh, a midwife at The Portland Hospital, London..
To work out the length of your menstrual cycle, count from the day your period normally starts to the day before your next period. The average cycle is 28 days.
Ready to brush off your GCSE maths? Take the first date of your last normal period, add seven days to that number. Take that date, add nine months, and you get your due month. Simple! Although, don’t be surprised if you add back and find you didn’t have sex on that exact date...
All babies grow at an individual rate and your due date is only an estimation, so be as prepared as you can be for a slightly-earlier-than-expected surprise, or carrying your baby for a little longer than that date you now have fixed in your head.
Keep in mind that women with irregular cycles may have difficulty calculating their due dates (the LMP method is far from a perfect science), so if you fall in that camp talk to your doctor to get the best estimate of your due date.
How likely is it my baby will be born on their due date?
As we mentioned above, only 4% of babies are born on their due date. Your due date is calculated from the end of your last period, plus 40 weeks or 280 days. That said, it is very likely your baby will arrive a couple of weeks either side of your due date, so it's a good idea to keep this date in mind and get prepared!
Pregnancy normally lasts from 37 to 42 weeks. It can be tricky at first to work out how to count your pregnancy in weeks and months, as when we measure your pregnancy from the start of your last period, your baby is actually two weeks younger than the pregnancy start date, otherwise referred to as the 'gestational age'. So, this means when your doctor tells you you're four weeks pregnant, your baby's gestational age is actually two weeks.
It’s not as simple as assuming your full-term pregnancy is the day you hit 40 weeks pregnant. In fact, your full-term pregnancy is considered to be anywhere from 38 to 42 weeks. Yes, it’s a due month.
‘On average pregnancy takes 40 weeks (or 10 lunar calendar months) from the first day of your menstrual cycle or 38 weeks from conception, but there isn’t an exact science to working out your due date,’ says Teresa.
At your dating scan, otherwise known as your 12-week scan, your midwife will be able to give you a more accurate guide to your due date. You will normally have a dating scan between 10-14 weeks pregnant. During the scan, the sonographer will look at how developed your baby is and measure the length of your baby from his head to his bottom, which helps them to give you an EDD (estimated due date) based on how far along in your pregnancy you are.
They will also check you are only expecting one baby, not two, and that your baby is developing in the right place.
Trimester means 'three months', so your pregnancy will be divided into three trimesters. Your first trimester will be from conception to thirteen weeks and six days. Your second trimester is from 14 weeks to 27 weeks and six days. Your third trimester is from 28 weeks to when you give birth.
Yes! Your due date can change due to a multitude of reasons, including incorrect calculations in the early weeks, or baby developments suggest your baby is further along (or less developed) in later scans, including your levels of alpha-fetoprotein (AFP), a protein made by the baby, being outside the usual range. If you have any questions or worries talk to your doctor.
Whether you are hankering for a summer baby or fancy not giving birth on Christmas day, you may be looking to 'plan your due date'. It's verging on impossible to plan your due date exactly, even if you are lucky enough to fall pregnant when you want to. As echoed throughout the article, only 4% of babies are born on their due date, so even if you have fallen pregnant in your chosen month, it's hard to determine which day/week your little one will arrive. There are some natural ways to induce labour, however, which you may want to bookmark for when the time arrives!
- Choose a doctor or midwife: You will be seeing a lot of your practitioner over the next 9 months, so have a look around at who would be a good match. Prenatal care providers often schedule a meeting for when you are 8 weeks pregnant.
- Confirm you're pregnant: If you've only gone by early pregnancy symptoms or a gut-feeling you're pregnant, take a test or visit a doctor to confirm.
- Start thinking about names: Check out our baby names generator, which is full of wonderful name inspiration (from Harry Potter to old-fashioned!) to get you excited for your new arrival
- Use our Chinese Gender Predictor: This chart, found in an ancient tomb near Beijing more than 700 years ago, is said to be 90% accurate in predicting your baby's gender (which is better than the 50/50 odds of how high your bump is, right?)
- Join a Facebook group: Be sure to join our Facebook group #mumtribe, which is a lovely community of mums sharing their motherhood journeys and reminding each other, no one is perfect!
- Get clued up on maternity leave: Whether you’re a self-employed mum-to-be or planning on returning to work once your baby’s born, it’s sensible to know exactly where you stand on maternity pay and benefits.
- Enjoy alone time with your partner (if you have one): If you want to keep schtum about your news until the 12-week scan, you and your partner can still have fun with the we-know-something-you-all-don’t-know excitement
Page last reviewed: 07/05/2019
Next review due: 07/05/2020
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