Pregnancy Due Date Calculator
Estimate your due date and current pregnancy week from your last period.
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How it works
The estimate uses Naegele's rule: a due date roughly 280 days (40 weeks) after the first day of your last menstrual period (LMP). If you prefer, enter a known conception date and it adds 266 days instead. For irregular cycles you can adjust for a cycle length other than 28 days. The tool also reports how many weeks and days pregnant you are today and which trimester that falls in. Date math uses date-fns. This is an estimate — only an ultrasound and your provider can confirm dates.
dueDate = LMP + 280 days (Naegele's rule)
Common use cases
- Getting an estimated due date early in pregnancy.
- Tracking your current gestational week and trimester.
- Adjusting the estimate for a longer or shorter menstrual cycle.
Frequently asked questions
How accurate is the due-date estimate?
Naegele's rule is a standard estimate, but only about 4% of births happen exactly on the due date. An early ultrasound is more precise, especially for irregular cycles. Treat this as a guide, not a guarantee.
What if my cycle is not 28 days?
You can enter your average cycle length. The tool shifts the estimate by the difference from 28 days, since ovulation — and therefore conception — tends to occur later in longer cycles.
Can I use a conception date instead of my last period?
Yes. Switch to conception mode and the due date is estimated as 266 days after conception, which is the same 40-week target measured from a known conception point.