Pregnancy due date calculator
Enter the first day of your last period to estimate your due date.
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How the due date is calculated
Naegele's rule adds 280 days (40 weeks) to the first day of your last period, assuming a 28-day cycle.
Due date = last period date + 280 days
Worked example
If your last period started on January 1st, your estimated due date would be October 8th.
Frequently asked questions
- What is Naegele's rule?
- It's the most common method to estimate a due date: add 280 days (40 weeks) to the first day of the last period.
- How accurate is the calculated date?
- It's an estimate. Only about 5% of babies are born exactly on the calculated date; most arrive within a 1-2 week range.
- What are pregnancy trimesters?
- Pregnancy is divided into three trimesters of roughly 13 weeks each.
- Does this replace medical care?
- No. It's a general guide only; pregnancy should be monitored by a healthcare professional with ultrasounds and check-ups.
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