Due Date Calculator UK

Calculate your estimated due date using one of five methods: last menstrual period, conception date, how far along you are, ultrasound dating, or IVF transfer. All calculations are free and no data is stored.

Enter the first day of your last period to calculate your due date using Naegele's rule.

The first day of your last menstrual period
21 to 45 days (default 28)
12 to 16 days (default 14)

How does the due date calculator work?

Most UK pregnancies are dated using Naegele's rule: adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14. Our calculator adjusts for different cycle lengths.

Your NHS dating scan, offered between 10 and 14 weeks, uses your baby's measurements to confirm or revise your due date. The scan is generally considered more accurate than LMP dating, particularly if your cycles are irregular.

The five calculation methods explained

Last Menstrual Period (LMP)

The most common method. Enter the first day of your last period and your cycle length. Due date = LMP + 280 days, adjusted for your cycle.

Conception Date

If you know when you conceived or ovulated, enter that date. We work back 14 days to find your equivalent LMP.

How Far Along?

Already know how many weeks pregnant you are? Enter your current gestational age and we calculate backwards to your due date.

Ultrasound Dating

Enter your scan date and the gestational age given by your sonographer. Particularly useful after your NHS dating scan.

IVF Transfer

For IVF pregnancies. Enter your embryo transfer date and whether you had a day 3, day 5 (blastocyst), or day 6 embryo transfer.

Frequently asked questions

How is my due date calculated?
Your due date is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This is known as Naegele's rule. Our calculator adjusts for cycle lengths other than 28 days.
Can I calculate my due date after IVF?
Yes. For IVF pregnancies, enter your embryo transfer date and embryo age. A day 5 blastocyst transfer adds 261 days to give your estimated due date. This is the most common method used in UK fertility clinics.
When will I get my due date confirmed?
Your NHS dating scan (offered at 10 to 14 weeks) will confirm your due date based on your baby's measurements. This scan date takes precedence over any calculator estimate.
What if my cycle is not 28 days?
Our Last Period method includes a cycle length adjustment. If your cycle is longer or shorter than 28 days, the calculator adjusts your due date accordingly. You can set your cycle length from 21 to 45 days.

Related tools

Ovulation Calculator→ Week by Week→ NHS Appointments→ Birth Plan→