NHS Pregnancy Due Date Calculator
Enter the first day of your last menstrual period (LMP) and your usual cycle length to estimate your due date and current pregnancy week.
How this NHS pregnancy calculator works
This pregnancy calculator gives an estimated due date (EDD) using the same basic approach commonly used in NHS settings: count forward from the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, the estimate is adjusted.
It is useful for planning and understanding your timeline, but it is still an estimate. Your dating scan and maternity team provide the most accurate clinical information.
What your results mean
Estimated due date (EDD)
Your EDD is the day your pregnancy reaches about 40 weeks. Most babies do not arrive exactly on this date, and that is normal. Birth can happen naturally in the weeks around it.
Gestational age today
The calculator shows your current pregnancy age in weeks and days. This can help you understand where you are in the pregnancy journey and when key appointments are likely to happen.
Estimated conception date
This is an estimate based on ovulation timing (roughly 14 days before your next period). It is not exact, especially if cycles are irregular.
How to use the calculator correctly
- Use the first day of your last period, not the day bleeding ended.
- Enter your average cycle length if known.
- If your periods are irregular, treat results as approximate only.
- Book your midwife appointment early even if your dates are uncertain.
NHS pregnancy timeline (typical)
First trimester (weeks 1 to 13)
- Contact maternity services as soon as pregnancy is suspected.
- Booking appointment often happens around 8 to 10 weeks.
- Dating scan is usually offered around 10 to 14 weeks.
Second trimester (weeks 14 to 27)
- Energy may improve for many people.
- Anomaly scan is commonly offered around 18 to 21 weeks.
- Routine antenatal checks continue.
Third trimester (weeks 28 to birth)
- Monitoring increases as due date approaches.
- Birth planning discussions become more detailed.
- Know signs of labour and when to call triage.
If your dates change after a scan
It is common for due dates to be adjusted after the dating scan. Ultrasound measurements in early pregnancy are often more accurate than period-based estimates, especially when cycle length varies.
Common questions
How accurate is a due date calculator?
It is a solid estimate, not a prediction. A due date is a planning tool rather than a guaranteed birth date.
Can I use this if I have irregular periods?
Yes, but with caution. Irregular cycles make LMP-based calculations less precise. Your scan is especially important.
What if I conceived via IVF?
IVF pregnancies are usually dated from embryo transfer and embryo age, so clinic-provided dates should take priority over general calculators.
Healthy pregnancy checklist
- Start or continue folic acid as advised by your healthcare team.
- Avoid smoking and alcohol.
- Review medicines with a pharmacist, GP, or midwife.
- Attend all antenatal appointments and scans.
- Seek urgent care for bleeding, severe pain, or concerning symptoms.