Due Date Calculator NHS

Calculate your baby's due date using the NHS method (Naegele's rule). Enter your last menstrual period (LMP) or ultrasound due date to get trimester dates and a visual pregnancy timeline. Informational only—consult an NHS midwife or doctor for prenatal care. Explore more tools on free calculators on CalculatorBolt.

Calculator

Calculation Method

Last Menstrual Period (LMP)

Ultrasound Due Date

First Day of Last Period

Start date of your last menstrual period

Average Cycle Length (days)

Typical cycle length (default 28 days)

Due Date

How Far Along

Current Trimester

Pregnancy Timeline

Key Dates

Import JSON

How it works

The NHS uses Naegele's rule to calculate your due date: Due Date = LMP + 280 days (40 weeks). This assumes a 28-day menstrual cycle with ovulation on day 14. We also calculate your likely conception date (Due Date - 266 days) and trimester dates. If you have an ultrasound due date from your dating scan, we use that as the primary estimate, as it's typically more accurate than LMP-based calculations.

Inputs explained

Calculation Method: Choose LMP (Last Menstrual Period) or Ultrasound Due Date.
First Day of Last Period: The start date of your last menstrual period before conception.
Average Cycle Length: Your typical menstrual cycle length (default 28 days). Cycles can range from 20-45 days.
Ultrasound Due Date: The estimated due date provided by your dating scan (usually done at 8-14 weeks).

Example

LMP = 1 January 2025
→ Due Date = 8 October 2025 (LMP + 280 days)
→ Likely Conception = 15 January 2025
→ 1st Trimester ends ~25 March 2025 (week 12)
→ 2nd Trimester: 26 March - 30 June 2025
→ 3rd Trimester: 1 July - 8 October 2025

Tips & notes

Only about 4% of babies are born on their exact due date. Most arrive within 2 weeks either side.
The full-term range is from 37 weeks to 42 weeks of pregnancy.
Book an appointment with an NHS midwife as soon as you know you're pregnant (ideally by 10 weeks).
Your dating scan (8-14 weeks) provides the most accurate due date estimate.
The NHS offers two ultrasound scans: dating scan (8-14 weeks) and anomaly scan (18-21 weeks).
Early pregnancy appointments include booking appointment (8-12 weeks) with blood tests and health checks.

NHS Pregnancy Milestones

Week	Milestone
8-12 weeks	Booking appointment with midwife
8-14 weeks	Dating scan (determines due date)
12 weeks	End of first trimester
16 weeks	Possible appointment with midwife
18-21 weeks	Anomaly scan (20-week scan)
25 weeks	Midwife appointment
28 weeks	Start of third trimester; blood tests
31-34 weeks	Midwife appointments
36 weeks	Midwife appointment; birth plan
37 weeks	Full term (baby ready to be born)
40 weeks	Due date
41+ weeks	Monitoring; possible induction

FAQs

The NHS adds 280 days (40 weeks) to the first day of the last menstrual period using Naegele's rule.

The NHS calculation still uses 280 days, but your ovulation date may vary. Ultrasound dating is more accurate for irregular cycles.

Contact your GP as soon as you find out you're pregnant to be referred to a midwife for your booking appointment.

No. Everything runs in your browser. Use Export or Share Link to save your dates.

Only about 4% of babies are born on their exact due date. Most births occur between 37-42 weeks.

First trimester: weeks 1-12; Second trimester: weeks 13-27; Third trimester: weeks 28-40+.

The NHS anomaly scan is typically offered between 18-21 weeks of pregnancy.

Full-term is between 37 weeks and 42 weeks. Babies born before 37 weeks are premature.

Disclaimer

Informational estimate only based on NHS guidelines. This is not a substitute for professional medical advice. Consult an NHS midwife or doctor for comprehensive prenatal care and monitoring throughout your pregnancy.