Pregnancy due date calculator
Enter a date
Your estimated due date and scan dates appear here. Nothing is stored or sent.
This is an estimate, not medical advice; your midwife or dating scan gives the confirmed date.
How to use it
- Choose what you know: the first day of your last period, the date of conception, or the date of an IVF embryo transfer.
- Enter the date. For a last period, set your usual cycle length if it isn't 28 days.
- Read the estimated due date, how many weeks pregnant you are today, and the dates of each trimester and the NHS scans.
How the due date is worked out
From your last period: the standard method (Naegele's rule) adds 280 days, or 40 weeks, to the first day of your last period. It assumes a regular 28-day cycle (Royal Berkshire NHS Foundation Trust). If your cycle is longer or shorter, ovulation is likely to be later or earlier, so the calculator moves the due date by the difference, as the NHS due date calculator does. Weeks of pregnancy are counted from your last period, so you are already about 2 weeks pregnant at conception.
Worked example: a last period starting on Thursday 1 January 2026 gives a due date of Thursday 8 October 2026. With a 32-day cycle, it moves 4 days later, to Monday 12 October 2026.
From conception: 266 days (38 weeks) are added to the conception date.
After IVF: the due date is 263 days after a 3-day embryo transfer, or 261 days after a 5-day blastocyst transfer (StatPearls: Estimated Date of Delivery; the same figures appear in American College of Obstetricians and Gynecologists Committee Opinion 700). For IVF pregnancies, maternity units usually keep the date given by the fertility clinic rather than changing it after a scan.
NHS scans and trimesters
- Dating scan: usually at around 10 to 14 weeks. It checks how far along the pregnancy is and sets your due date, which may differ from the date worked out from your period (NHS: 12-week scan).
- Mid-pregnancy scan: between 18 and 21 weeks, to check how the baby is developing (NHS: ultrasound scans).
- Trimesters: the NHS week-by-week guide puts the second trimester at weeks 13 to 27 and the third from week 28.
Your maternity service books the actual appointments. To count weeks from any date, use weeks from today or the date calculator.
Will the baby arrive on the due date?
Probably not. Pregnancy usually lasts between 37 and 42 weeks (NHS Best Start in Life), and only 4.4% of babies, fewer than 1 in 20, are born on their due date (Royal Berkshire NHS Foundation Trust, 2026). Treat the due date as the middle of a window of several weeks. For a countdown, see days between dates.
This calculator is not medical advice; your midwife or dating scan gives the confirmed date. If you have bleeding, pain or any worry about your pregnancy, contact your midwife or maternity unit, or call NHS 111.
Frequently asked questions
How is my due date calculated?
By adding 280 days (40 weeks) to the first day of your last period, adjusted if your cycle is longer or shorter than 28 days. Your dating scan then gives the confirmed date.
How many weeks pregnant am I?
Count the weeks from the first day of your last period, not from conception. Enter that date in the calculator and it shows the weeks and days today, for example 13+1 for 13 weeks and 1 day.
Can my due date change?
Yes. The dating scan at around 10 to 14 weeks measures the baby and may move the due date. The scan date is the one your maternity care uses.
How is an IVF due date worked out?
Add 263 days to the date of a 3-day embryo transfer, or 261 days to a 5-day blastocyst transfer. Your fertility clinic will normally give you the date.
How many babies are born on their due date?
Only about 4.4%, fewer than 1 in 20. Most babies arrive between 37 and 42 weeks of pregnancy.
Is this medical advice?
No. It is an estimate based on standard rules. Your midwife or dating scan gives the confirmed date.