The NHS Pregnancy Calculator is a tool provided by the UK’s National Health Service (NHS) to help estimate your due date and track the progress of your pregnancy. It is based on the date of your last menstrual period (LMP) and assumes a typical 28-day menstrual cycle.

How It Works:

1. Last Menstrual Period (LMP):
   • The calculator uses the first day of your last menstrual period as the starting point.
   • Pregnancy is calculated as 40 weeks (280 days) from the first day of your LMP.
2. Estimated Due Date (EDD):
   • The due date is calculated by adding 280 days (40 weeks) to the first day of your LMP.
   • Alternatively, you can subtract 3 months from the first day of your LMP and add 7 days (Naegele’s Rule).
3. Adjustments for Cycle Length:
   • If your menstrual cycle is longer or shorter than 28 days, the due date may be adjusted accordingly.

Example Calculation:

• If your LMP started on January 1st, your estimated due date would be October 8th (January 1 + 9 months + 7 days).

Key Points:

• The calculator provides an estimate and not an exact date. Only about 5% of babies are born on their due date.
• If you know the date of conception (e.g., through IVF or tracking ovulation), the due date can be calculated more accurately.
• An ultrasound scan during pregnancy (usually around 8–14 weeks) can provide a more precise due date based on the baby’s size and development.

How to Use the NHS Pregnancy Calculator:

1. Visit the NHS website or use their online tools.
2. Enter the first day of your last menstrual period.
3. The calculator will provide your estimated due date and a week-by-week pregnancy timeline.