Pregnancy Due Date Calculator UK

Understanding Your Due Date & NHS Antenatal Care

Your estimated due date (EDD) is a guide, not a guarantee. Understanding how it is calculated and what to expect from NHS antenatal care helps you prepare for a healthy pregnancy.

Naegele's Rule: The Standard Calculation

The most widely used method for calculating due dates is Naegele's rule, developed by German obstetrician Franz Karl Naegele in the 19th century. It works by adding 280 days (40 weeks) to the first day of your last menstrual period, assuming a 28-day cycle with ovulation on day 14. For longer or shorter cycles, our calculator adjusts the ovulation date accordingly. The NHS uses this method as the baseline, with the 12-week dating scan used to refine the estimate.

IVF Due Date Calculation

For IVF pregnancies, due dates are calculated from the embryo transfer date, adjusted for the age of the embryo. A day 5 blastocyst transfer adds 261 days to the transfer date (because the embryo is already 5 days old). A day 3 cleavage-stage transfer adds 263 days. IVF due date calculations are typically more accurate than LMP-based calculations, because the conception date is precisely known. In 2024, around 68,000 IVF cycles were performed in the UK (HFEA data), with a live birth rate of approximately 25–32% depending on age.

NHS Antenatal Appointments

The NHS recommends the following schedule of antenatal appointments for first-time mothers:

UK Maternity Rights and Pay

Understanding your maternity rights helps you plan financially and practically for your new arrival:

• Statutory Maternity Leave: Up to 52 weeks (26 weeks ordinary, 26 weeks additional). You can take this from 11 weeks before your due date.
• Statutory Maternity Pay (SMP): As of April 2025, 90% of average weekly earnings for 6 weeks, then £184.03/week for 33 weeks (total 39 weeks).
• Maternity Allowance: For those who don't qualify for SMP — up to £184.03/week for 39 weeks.
• Shared Parental Leave (SPL): Parents can share up to 50 weeks of leave and 37 weeks of pay between them.
• Paternity Leave: Partners are entitled to 1 or 2 weeks of paid paternity leave at £184.03/week (or 90% of earnings if lower).
• Antenatal appointments: You have the right to paid time off for all NHS-recommended antenatal appointments.
• Health and Safety: Your employer must conduct a risk assessment and adjust working conditions if necessary during pregnancy.

Gestational Age vs Fetal Age

Gestational age is counted from the first day of your LMP, while fetal age (fertilisation age) counts from the actual moment of conception — typically 2 weeks later. This means NHS professionals describe a pregnancy as being 2 weeks further along than the actual age of the embryo/fetus. All NHS appointments, scan dates, and medical records use gestational age. When midwives or doctors say your baby is "40 weeks", the embryo has actually been developing for approximately 38 weeks from fertilisation.

Premature Birth in the UK

Approximately 60,000 babies are born premature in the UK each year, representing around 8% of all births. Full term is defined as 37–42 weeks gestation. Births before 37 weeks are considered premature, with sub-categories ranging from extremely premature (before 28 weeks) to late premature (34–36 weeks). Advances in neonatal intensive care mean babies born at 24 weeks now have a survival rate of around 55%, rising to over 95% at 28 weeks. The neonatal charity Bliss UK provides support for families of premature babies. If you experience any signs of premature labour — such as regular contractions before 37 weeks, lower back pain, or a change in vaginal discharge — contact your midwife immediately or call 999.

Frequently Asked Questions