Pregnancy Due Date Calculator
Enter the first day of your last period, or your conception date, to estimate your due date.
Your details
Result
Fill in the fields to see your result.
Good to know: Only about 5% of babies arrive on the due date. Most are born within two weeks either side.
Please note: General estimate for information only. This is not medical advice, diagnosis or treatment, and it may not suit your age, health, medication or pregnancy. Never use it to make a medical decision. Talk to a doctor or other qualified health professional about your own situation, and in an emergency call your local emergency number.
About this tool
Estimate your pregnancy due date from your last menstrual period (LMP) or conception date — for expectant parents.
Formula
Due date = LMP + 280 days (40 weeks). From conception: add 266 days (38 weeks).
Reference values
- Full-term pregnancy = 40 weeks from LMP
- Conception occurs ~14 days after LMP
- Due dates have ±2 week accuracy
Questions people ask
How is the due date worked out?
Last period plus 280 days (40 weeks). From conception, add 266 days.
How accurate is it?
It is an estimate. Your midwife or doctor may adjust it after an ultrasound scan.
What if my cycle isn't 28 days?
The estimate assumes a 28-day cycle. Tell your care provider if yours differs.
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How we calculate this
We use the standard published formula or definition for this calculation, and we show the working so you can check it. Source: Naegele's rule (LMP + 280 days).
Spotted a mistake? Tell us and we'll check it. How we check our calculators