Only about one baby in twenty arrives exactly on the due date - it is the midpoint of a window, not a deadline. The tool also shows today's gestational age, the current trimester, the estimated conception date and the key milestone dates for each trimester. Always confirm dates with your midwife or doctor, who may adjust the estimate after a dating scan.
Calculator
Formula used
EDD = first day of last period + 280 days · from conception: + 266 days
How to use the Pregnancy Due Date Calculator
- Choose whether to calculate from your last period, conception or an ultrasound date.
- Enter the date and, for LMP, your average cycle length.
- Read the estimated due date and gestational age.
- Check the milestone table for trimester boundaries.
About this tool
The Pregnancy Due Date Calculator is built for speed and accuracy: every calculation runs in your browser, so your data never leaves your device and the result updates as you type. It works equally well on a phone, a tablet or a desktop, and it is free to use as many times as you like.
Common use cases
- Estimating a due date after a positive test.
- Converting an ultrasound date into a conception window.
- Working out gestational age at any point in pregnancy.
- Planning around trimester milestones.
Tips for the best result
- Use the latest figures you have - even a small change in rate or term can shift the outcome by hundreds.
- For annual figures, divide by 12 to get a monthly number you can compare with the result.
- Bookmark this page and revisit the calculation as the inputs change.
Frequently asked questions
How accurate is the due date?
Dating from a first-trimester ultrasound is accurate to about five to seven days; dating from the last period is usually within two weeks because cycle length and ovulation vary.
Does cycle length change the result?
Yes. Naegele's rule assumes a 28-day cycle. The calculator adds the difference between your cycle length and 28 days to correct for it.
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