Pregnancy Due Date Calculator
Estimate your due date, current week and trimester.
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This calculator uses the standard method that clinics use: your estimated due date is 280 days, or 40 weeks, from the first day of your last menstrual period. Enter that date and you will see your estimated due date, how many weeks and days along you are today, which trimester you are in, and the key milestone dates along the way. It is a helpful reference between appointments.
How a due date is worked out
The standard method counts 280 days, or 40 weeks, from the first day of your last menstrual period. It assumes a regular 28 day cycle with ovulation around day 14, which is why it is an estimate rather than a fixed date. If your cycles are longer, shorter or irregular, the figure it produces can be out by a week or more in either direction.
What the date actually means
Very few babies arrive exactly on their due date. Only around one in twenty does. A full term birth is anywhere from 37 to 42 weeks, so the due date is better understood as the centre of a window than as a deadline. An early ultrasound, usually in the first trimester, dates a pregnancy more accurately than the calendar method, and if the two disagree your doctor will normally go with the scan.
Please read this part
- This calculator is a general estimate and is not medical advice.
- Your midwife or doctor's date is the one that matters, particularly after a dating scan.
- It assumes a regular 28 day cycle, so irregular cycles reduce its accuracy.
- It does not apply to IVF pregnancies, which are dated from the transfer instead.
- Speak to a healthcare professional about anything that concerns you. Do not rely on a web tool for decisions about a pregnancy.
How to use Pregnancy Due Date Calculator
- 1
Enter the first day of your last menstrual period.
- 2
Adjust your average cycle length if it is not 28 days.
- 3
See your estimated due date and current week.
Frequently asked questions
It is a standard estimate. Only about 4 percent of babies arrive exactly on the due date, and an ultrasound gives a more precise date.