Pregnancy Due Date Calculator
Estimate your baby’s due date from your last period, conception date or IVF transfer date, and see how many weeks pregnant you are today.
This is an estimate. Only about 1 in 25 babies arrive on their due date, and most are born within two weeks either side. Your doctor or midwife may adjust the date after an early ultrasound scan.
How your due date is worked out
Pregnancy is usually counted from the first day of your last menstrual period (LMP), about two weeks before conception. A full-term pregnancy lasts around 280 days, or 40 weeks, from that date. This is known as Naegele’s rule.
- Last period: due date = first day of last period + 280 days. If your cycle is longer or shorter than 28 days, the date is moved by the difference.
- Conception date: due date = conception + 266 days.
- IVF transfer: due date = transfer date + 266 days − the age of the embryo in days. A day-5 blastocyst transfer gives transfer + 261 days.
Trimesters
- First trimester: weeks 1 to 13
- Second trimester: weeks 14 to 27
- Third trimester: week 28 until birth
How accurate is a due date?
A due date is an estimate. Only around 4% of babies are born on the exact day, and most arrive between 37 and 42 weeks. An early dating ultrasound, usually between 8 and 14 weeks, measures the baby and is often used to confirm or adjust the date.
When to talk to a professional
This calculator gives general information only. Your doctor, midwife or clinic will give you a due date based on your own history and scans. Contact them straight away if you have bleeding, severe pain, reduced movements later in pregnancy, or any other concern.
Due Date Calculator FAQs
Answers about due dates, weeks and trimesters.
How is my due date calculated?+
Usually by adding 280 days (40 weeks) to the first day of your last period. The calculator adjusts this for longer or shorter cycles, or uses your conception or IVF transfer date instead.
How many weeks pregnant am I?+
Pregnancy weeks are counted from the first day of your last period, not from conception. The calculator shows your current week and day based on today's date.
What if my cycle is irregular?+
The last-period method is less reliable with irregular cycles. An early ultrasound scan gives a more accurate date, so ask your doctor or midwife.
Can my due date change?+
Yes. It is often adjusted after the first ultrasound if the baby's measurements suggest a different date.
Is my information saved?+
No. Everything is calculated in your browser and nothing you enter is sent to our servers.
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