Calculated arrival cycle (40-week estimate)
| Conception | Expected Arrival |
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Human gestation follows a standard Gaussian distribution. While the 40-week (280-day) estimate serves as a clinical anchor for timing, statistical reality shows that only 4% of infants arrive on their exact calculated date. Approximately 90% of deliveries occur within a variance window spanning 10 days before to 10 days after the estimate. This inherent biological deviation suggests that the "due date" is a mathematical probability center rather than a fixed biological event.