Pregnancy due date calculator

How does the pregnancy due date calculator work?

Our pregnancy calculator uses the date of your last menstrual period (LMP) to estimate your due date. It assumes a typical 28-day cycle, with ovulation happening around day 14.

If you know the exact date of conception, you can enter that instead, though for many people, the LMP is a more practical reference.

Pregnancy is estimated to last 280 days (40 weeks) from the first day of your last period. Your due date is not an exact science, but it gives you a useful timeframe for planning antenatal care and preparing for birth.

Can I use the calculator if my cycle is irregular?

Yes, but if your cycle is significantly shorter or longer than 28 days, it may affect the estimated due date. For the most accurate results, use:

• The date of conception (if known)

• An early ultrasound scan, which is often more reliable for dating your pregnancy

If you're unsure, speak to your midwife or GP who can offer guidance based on your personal history and scan results.

Is my due date guaranteed?

Not exactly, only around 5% of babies are born on their due date. Most arrive between 37 and 42 weeks of pregnancy. Your due date is best seen as a guide to help track your baby’s development and prepare for labour.

Your midwife or doctor will update your estimated due date if needed, especially after a dating scan in your first trimester.