Pregnancy Due Date Calculator
Due date, current week, and trimester milestones.
The standard 28-day assumption puts ovulation on day 14. A longer cycle pushes the due date later.
Only about 4% of babies arrive on their estimated date, and roughly 90% land within two weeks of it. A first-trimester ultrasound dates a pregnancy more accurately than this calculation.
Estimated due date
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How the Pregnancy Due Date Calculator works
Due dates are estimated with Naegele's rule: 280 days from the first day of your last menstrual period. Only about 4% of babies arrive on the exact date, so treat it as the centre of a two-week window rather than a deadline.
How the 40 weeks are counted
Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.
Frequently asked questions
How is a due date calculated?
Naegele's rule adds 280 days (40 weeks) to the first day of your last menstrual period, which assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, this calculator shifts the date by the difference.
Why does pregnancy count from my last period?
Because the LMP date is something you can actually observe, while conception usually is not. It means the first two weeks of your '40 weeks pregnant' occurred before conception — gestational age runs about two weeks ahead of embryonic age.
How accurate is the estimated due date?
Roughly 4% of births happen on the estimated date, about 60% within a week of it, and around 90% within two weeks. A first-trimester ultrasound dates a pregnancy more accurately than LMP, and your provider may revise the date accordingly.
When do the trimesters start and end?
First trimester is weeks 1-13, second is weeks 14-27, and third is weeks 28 through birth. A pregnancy is considered full term from 39 weeks, early term from 37, and post-term after 42.