预产期计算器
宝宝什么时候出生？
This calculator estimates your due date based on the first day of your last menstrual period (LMP), a standard method used by healthcare providers as a starting reference point for pregnancy dating.
How it's calculated
The estimate uses Naegele's rule: due date = LMP + 280 days (40 weeks), adjusted for your average cycle length if it differs from the standard 28 days.
Example
If your last period started on a given date and your cycle is 28 days, your estimated due date falls 280 days later. A 32-day cycle would shift the estimate about 4 days later.
常见问题
How accurate is this estimate?
Only about 5% of babies are born exactly on their estimated due date. Most births occur within a window of roughly two weeks before or after this date.
Why does cycle length matter?
Naegele's rule assumes a standard 28-day cycle with ovulation around day 14. Longer or shorter cycles shift the actual conception date, so adjusting for cycle length improves the estimate.
Should I rely on this instead of a medical ultrasound?
No. This is a general estimate for reference only. An early ultrasound performed by a healthcare provider gives a more accurate dating of the pregnancy.