How to calculate your pregnancy estimated due date?

'I want a scan but just not sure how many weeks I am or when my due date is.'

We hear this time and time again from our patients and understandably for any new expectant parent finding out your pregnant is a lot to take in but then working through the jumble of last period dates, ovulation date, current gestation date, and so on can be daunting to say the least.

We have listened to your feedback and developed a super simple to use pregnancy due date calculator - which not only lets you know your estimated due date but also the current stage of your pregnancy in weeks and days as well as your estimated date of ovulation/conception.

Click on the button below to be taken to the pregnancy calculator:

https://thescanclinic.co.uk/pregnancy-due-date-calculator

How is my pregnancy due date calculated?

A typical pregnancy normally lasts between 37 weeks to 42 weeks from the first day of your last period. We use the first day of your last period as there's no reliable way to know for sure exactly when you ovulated and conceived, unless you have been tracking your ovulation. Most women ovulate about two weeks after the first day of their period, and conceive shortly afterwards. That's why your due date is calculated based on the date of your last period instead.

To work out your estimated due date we also need to know the the length of your menstrual cycle, for some women there menstrual cycle can be regular or irregular. To calculate your menstrual cycle length - count the first day from your last period to the day before your next period, the average cycle length is 28 days which is what the default setting on the calculator. If your periods are usually regular then you can leave this as 28 days however if they are irregular then enter the number of days it is or work out the average over the last few months and enter this.

Our calculator uses both the period date and average cycle length 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 4% 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. As part of your routine NHS maternity care you will receive a dating scan when you are typically around 12 weeks pregnant that will give you a more accurate guide to your due date. You can choose to have a private pregnancy scan which can help guide you on your current stage of pregnancy and estimated due date which are available from 6 weeks pregnant- you can see our full range of pregnancy scans here.

Note: Any private pregnancy scan performed prior to your NHS dating scan can only give you an indication of your current pregnancy stage and due date and will not replace the due date and date of your pregnancy given to you ar your NHS scan as this becomes your universal date and will be used in any future scans.