Due Date Calculator
A due date is estimated as 40 weeks (280 days) from the first day of your last period, adjusted if your cycle is longer or shorter than 28 days.
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The math behind it: Due Date
due date = first day of last period + 280 days + (cycle length - 28)
This is Naegele's rule. A due date is an estimate: most babies arrive within two weeks either side. An early ultrasound scan gives a more reliable date and may replace this one.
Common questions
How accurate is a due date?
Only around 4% to 5% of babies are born on their due date. Full term runs from 39 weeks to 40 weeks 6 days.
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