Pregnancy Due Date Calculator
Estimate your baby’s arrival and track your pregnancy journey. Calculate your estimated due date (EDD) and current week based on your last menstrual period or conception date.
Calculate Your Estimated Due Date
Enter your details below to instantly calculate your estimated due date (EDD), current pregnancy week, and key upcoming milestones.
Calculator Inputs
Provide your dates to generate a personalised pregnancy timeline
| Trimester | Weeks | Key Developments |
|---|---|---|
| First Trimester | Weeks 1 – 12 | Major organs form, heartbeat detectable, dating scan occurs. |
| Second Trimester | Weeks 13 – 27 | Movement felt (quickening), anomaly scan (18–21 weeks), gender may be visible. |
| Third Trimester | Weeks 28 – 40+ | Rapid weight gain, baby moves into head-down position, preparation for labour. |
Based on a standard 280-day pregnancy
Key Factors in Due Date Calculation
Understanding how your due date is calculated helps you know what to expect during your early prenatal appointments.
Naegele’s Rule
This is the standard medical formula used globally. It calculates the due date by taking the first day of your Last Menstrual Period (LMP), adding 7 days, and subtracting 3 months (equivalent to 280 days or 40 weeks).
Cycle Length Adjustment
Naegele’s rule assumes a perfect 28-day cycle with ovulation on day 14. If your average cycle is longer or shorter, the calculator adjusts the due date accordingly, as ovulation (and therefore conception) happens later or earlier.
Ultrasound Dating
Your midwife will offer a dating scan between 8 and 14 weeks. If the baby’s measurements (Crown-Rump Length) differ from your LMP date by more than a few days, the NHS will officially update your Estimated Due Date to match the scan.
Pregnancy Calculator FAQ
Answers to the most frequently asked questions about pregnancy due dates and NHS timelines in the UK.
A due date calculator provides a highly reliable estimate, but only about 4% of babies are born on their exact due date. It is best viewed as a 4-week window (from 38 to 42 weeks) when your baby is likely to arrive. An early dating ultrasound (between 8 and 14 weeks) is the most accurate way to confirm your due date.
LMP (Last Menstrual Period) is the standard medical method, assuming a regular 28-day cycle where ovulation occurs around day 14. If you know the exact date of conception (e.g., through IVF or ovulation tracking), using the conception date can provide a more precise estimate, as it adds exactly 266 days (38 weeks) to that date.
In the UK, the NHS typically offers a ‘dating scan’ between 8 and 14 weeks of pregnancy. This scan confirms your due date, checks for a heartbeat, and determines if you are expecting more than one baby. Later, an anomaly scan is offered between 18 and 21 weeks.
Yes. If your menstrual cycles are irregular, or if the measurements from your first-trimester dating ultrasound differ significantly from the date calculated by your LMP, your midwife or doctor will adjust your Estimated Due Date (EDD) to match the ultrasound measurements.