Tommy's PregnancyHub

Pregnancy due date calculator

Just found out you’re pregnant? Work out when your baby is due with our pregnancy due date calculator.
Due Date Calculator

Pregnancy due date calculator

How do I use the pregnancy calculator?

To find out your due date, you just need to select the date of the first day of your last period on our pregnancy calculator tool, adjust your average cycle length and click 'submit’. Your cycle length is the number of days between your periods, counting the first day of your period until the day before your next period starts. 

You will then receive your estimated due date and the option to sign-up to our pregnancy email. This weekly email gives you fun pregnancy facts, useful tips and great recipe ideas to help you and your baby have the healthiest possible pregnancy.

Are you in early pregnancy? Find out all you need to know about pregnancy from week 4 onwards.

What if I have irregular periods?

If you were having irregular periods before you got pregnant, you can still use the pregnancy calculator. Just choose your average cycle length. But bear in mind that an ultrasound will be the most accurate way of predicting your due date.

How accurate is the due date?

The pregnancy calculator gives you an approximate due date. It is worked out by adding 280 days (40 weeks) to the first day of your last menstrual period. This is based on a 28-day cycle but is adjusted for longer or shorter cycles.

Your period and ovulation are counted as the first 2 weeks of pregnancy. If you have the baby on your due date, your baby has been growing for 38 weeks, not 40, but you are still classed as 40 weeks pregnant. 

Remember that only around 5% of babies are born on their due date so it’s just an estimation.  

Will I get a more accurate due date later in the pregnancy?

You will have your first appointment with the midwife, the 'booking appointment', by 10 weeks.  At that appointment, you will be offered an ultrasound scan – this is often called the dating scan.  

This scan will check how many weeks pregnant you are and work out a more accurate due date. You’ll also be able to find out whether you’re having more than 1 baby and how your baby is developing.  

But if you're impatient to know when your baby will arrive, our due date calculator can give you an estimated due date now! 

What should I do next?

If you don’t already have a midwife, you may be able to self-refer to your local maternity unit directly for your antenatal care. Visit your local hospital’s website to find out more.

Speak to your GP if you can’t self-refer or if you think your pregnancy may be high-risk. For example, if you have a long-term condition, had complications in a previous pregnancy or experienced a late miscarriage or stillbirth. Your GP will tell the midwifery team you are pregnant.

You will be given a date for your first appointment with a midwife. This should happen before you are 10 weeks pregnant. 

We know pregnancy can be an overwhelming time. We created our Healthy Pregnancy tool to try to take away some of this anxiety by giving you a personalised set of tips for your pregnancy. 

  • Mongelli M. 2016. Evaluation of gestation. Medscape. 
  • NICE [NG201]. Antenatal care. Published: August 2021.
  • NHS. 12-week scan. Available at: www.nhs.uk/pregnancy/your-pregnancy-care/12-week-scan/ Page last reviewed: 18 December 2020, Next review due: 18 December 2023.
Review dates
Reviewed: 09 August 2022 | Next review: 09 August 2025