Due Date Calculator
Estimate a due date and see how far along a pregnancy is.
How due dates are worked out
A full-term pregnancy is counted as 40 weeks, or 280 days, from the first day of the last period. This is known as Naegele’s rule. If you know the conception date, the estimate is 266 days (38 weeks) later. If your cycle is longer or shorter than 28 days, the estimate shifts to match.
Example
A last period starting on 1 August 2026, with a 28-day cycle, gives an estimated due date of 8 May 2027. Conception would be around 15 August 2026.
Please remember
- Only about 1 in 20 babies is born on the estimated date. Many arrive in the weeks before or after.
- A dating scan can change the estimate, and your doctor or midwife’s date is the one to follow.
- This tool is for general information and is not medical advice.
Frequently asked questions
How is the trimester decided?
The first trimester runs to the end of week 13, the second from week 14 to week 27, and the third from week 28 until birth.
What if my cycle is irregular?
The estimate is less reliable. Ask your doctor or midwife for an ultrasound dating, which is more accurate.
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