Calculator
Pregnancy due date
An estimate from the first day of the last period.
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Method and limits
| Formula | Naegele’s rule: last menstrual period + 280 days, adjusted for cycle length away from 28 days. |
|---|---|
| Who it is for | Anyone with a known last menstrual period date and a reasonably regular cycle. |
| Source | Naegele’s rule |
| Method validated | No — not yet checked against the cited source by a person |
What this cannot tell you. An estimate with a wide spread — most births happen within about two weeks either side, and a dating scan is considerably more accurate. Treat the date as a midpoint, not an appointment.